feat: Add Bootstrap 4 Theme support (#1938)

* new(theme): initial setup for bootstrap-4 using react-bootstrap

* create bootstrap-4 textfield widget

* add * for required fields

* chore: fixed formatting issue

* tests: added tests for textWidget

* create Radio Widget

* minor fix

* removed margin-bottom to fix description/helpertext margin

* add bootstrap-4 updown widget

* Update packages/bootstrap-4/src/RadioWidget/RadioWidget.tsx

Co-authored-by: Jani Eväkallio <jani.evakallio@gmail.com>

* Update RadioWidget.tsx

* Update packages/bootstrap-4/src/RadioWidget/RadioWidget.tsx

Co-authored-by: Jani Eväkallio <jani.evakallio@gmail.com>

* Update packages/bootstrap-4/src/RadioWidget/RadioWidget.tsx

Co-authored-by: Jani Eväkallio <jani.evakallio@gmail.com>

* add bootstrap-4 URL widget

* add email, password, select. modified text, field template for fixes and support. refactored form component

* add errorlist component, modified others for required attribute support

* code fixes

* chore: resolve conflicts

* feat(bootstrap-4): added descriptionField

* chore: removed style tag and using classname for styling

* update: changed typedef and using fieldProps

* chore: fix tests

* types: descriptionField extending from FieldProps

* tests: updated tests and typinh

* feat(bootstrap-4): titleField Component

* test: updated test and types for titleField

* chore: fixed merge conflicts

* chore(bootstrap-4): removed fontawesome icons

* feat(bootstrap-4): checboxesWidget

* style(bootstrap-4): fixed inconsistency of the buttons (fixes #52)

* chore: resolved merge conflict

* chore: upate the tests and added mock handlers

* test(bootstrap-4): added tests for DateWidget

* test(bootstrap-4): added tests for DateTimeWidget

* chore: fixed tests and components

* fix: temporary playground fix

* feat(bootstrap-4): added textAreaWidget

* chore: tests for testAreaWidget

* chore: added margin left

* feat(bootstrap-4): checkboxWidget [WIP]

* test: added tests for checkboxWidget

* chore: added suggestions and todos

* update README.md

* chore: uncomment temp changes

* chore: deleted extra files

* minor fixes

* chore: suggestion applied

* Fix ObjectFieldTemplate

Missed this patch while doing some cleaning-up of code

* add placeholder to select widget

* test: updated tests for placeholder in select widget

* fix CI build

* update deps

* suggestion fixes pt.1

* suggested changes fix pt.2

* fix suggested changes pt.3

* fix: fixed the inconsistency in the radio and select widget

* snapshot fixes

* snapshot fixes pt.2

* chore: small changes and test update

Co-authored-by: Anix <anik220798@gmail.com>
Co-authored-by: Jani Eväkallio <jani.evakallio@gmail.com>
Co-authored-by: Ashwin Ramaswami <aramaswamis@gmail.com>

packages/bootstrap-4/.gitignore

@@ -0,0 +1 @@
+.rts2_**

packages/bootstrap-4/README.md

@@ -0,0 +1,110 @@
+<!-- PROJECT LOGO -->
+<br />
+<p align="center">
+  <a href="https://github.com/rjsf-team/react-jsonschema-form">
+    <img src="./react-bootstrap-4-logo.png" alt="Logo" width="140" height="120">
+  </a>
+
+  <h3 align="center">@rjsf/bootstrap-4</h3>
+
+  <p align="center">
+  Bootstrap-4 theme, fields and widgets for <a href="https://github.com/mozilla-services/react-jsonschema-form/"><code>react-jsonschema-form</code></a>.
+    <br />
+    <a href="https://react-jsonschema-form.readthedocs.io/en/latest/"><strong>Explore the docs »</strong></a>
+    <br />
+    <br />
+   <a href="https://rjsf-team.github.io/react-jsonschema-form/">View Playground</a>
+    ·
+    <a href="https://github.com/rjsf-team/react-jsonschema-form/issues">Report Bug</a>
+    ·
+    <a href="https://github.com/rjsf-team/react-jsonschema-form/issues">Request Feature</a>
+  </p>
+</p>
+
+<!-- TABLE OF CONTENTS -->
+
+## Table of Contents
+
+- [About The Project](#about-the-project)
+- [Getting Started](#getting-started)
+  - [Prerequisites](#prerequisites)
+  - [Installation](#installation)
+- [Usage](#usage)
+- [Contributing](#contributing)
+- [Contact](#contact)
+
+<!-- ABOUT THE PROJECT -->
+
+## About The Project
+
+
+Exports `bootstrap-4` theme, fields and widgets for `react-jsonschema-form`.
+
+### Built With
+
+- [react-jsonschema-form](https://github.com/mozilla-services/react-jsonschema-form/)
+- [Bootstrap-4](https://getbootstrap.com/docs/4.0/)
+- [Typescript](https://www.typescriptlang.org/)
+
+<!-- GETTING STARTED -->
+
+## Getting Started
+
+### Prerequisites
+
+- `react-bootstrap >= 1.0.1`
+- `@rjsf/core >= 2.2.0`
+
+```bash
+yarn add react-bootstrap @rjsf/core
+```
+
+### Installation
+
+```bash
+yarn add @rjsf/bootstrap-4
+```
+
+## Usage
+
+```js
+import Form from '@rjsf/bootstrap-4';
+```
+
+or
+
+```js
+import { withTheme } from '@rjsf/core';
+import { Theme as Bootstrap4Theme } from '@rjsf/bootstrap-4';
+
+const Form = withTheme(Bootstrap4Theme);
+```
+
+<!-- CONTRIBUTING -->
+
+## Contributing
+
+Read our [contributors' guide](https://react-jsonschema-form.readthedocs.io/en/latest/contributing/) to get started.
+
+<!-- CONTACT -->
+
+## Contact
+
+rjsf team: [https://github.com/orgs/rjsf-team/people](https://github.com/orgs/rjsf-team/people)
+
+GitHub repository: [https://github.com/rjsf-team/react-jsonschema-form](https://github.com/rjsf-team/react-jsonschema-form)
+
+<!-- MARKDOWN LINKS & IMAGES -->
+<!-- https://www.markdownguide.org/basic-syntax/#reference-style-links -->
+
+[build-shield]: https://github.com/rjsf-team/react-jsonschema-form/workflows/CI/badge.svg
+[build-url]: https://github.com/rjsf-team/react-jsonschema-form/actions
+[contributors-shield]: https://img.shields.io/github/contributors/rjsf-team/react-jsonschema-form.svg
+[contributors-url]: https://github.com/rjsf-team/react-jsonschema-form/graphs/contributors
+[license-shield]: https://img.shields.io/badge/license-Apache%202.0-blue.svg?style=flat-square
+[license-url]: https://choosealicense.com/licenses/apache-2.0/
+[npm-shield]: https://img.shields.io/npm/v/@rjsf/bootstrap-4/latest.svg?style=flat-square
+[npm-url]: https://www.npmjs.com/package/@rjsf/bootstrap-4
+[npm-dl-shield]: https://img.shields.io/npm/dm/@rjsf/bootstrap-4.svg?style=flat-square
+[npm-dl-url]: https://www.npmjs.com/package/@rjsf/bootstrap-4
+[product-screenshot]: https://raw.githubusercontent.com/rjsf-team/react-jsonschema-form/59a8206e148474bea854bbb004f624143fbcbac8/packages/bootstrap-4/screenshot.png