feat: add initial SDK library boilerplate and basic svelte LD SDK

[nosnibor89]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines (TBH yarn run contract-tests failed for me even in main)
• I have validated my changes against all supported platform versions

Related issues

No issue

Describe the solution you've provided

Introducing the new @launchdarkly/svelte-client-sdk package. Some of the details included in this PR are

1. Svelte Library Boilerplate
2. Basic Svelte SDK functionality:
   2.1 LDProvider component
   2.2 LDFlag component
   2.3 Svelte-compatible LD instance (exposes API to work with feature flags)

Describe alternatives you've considered

I don't know what to write here.

Additional context

This is the first of a series of PRs. Some of the following PR should be about

1. Adding Documentation for @launchdarkly/svelte-client-sdk
2. Adding Example project that uses @launchdarkly/svelte-client-sdk

[kinyoklion]

Hello @nosnibor89,

Thank you for the contribution.

Those contract tests aren't relevant to client-side SDKs, but they should all work correctly (and do run in CI and passed for your PR). When developing locally running yarn build in the root of the repo should get everything into a functioning state. (Builds all packages, and everything in the workspace will use local packages.) The contract tests do run a go binary downloaded from github, so that could cause problems for some configurations.

I won't be able to review this deeply this week, but hopefully I can next week.

Thank you,
Ryan

[nosnibor89]

Awesome @kinyoklion . Thanks for improving and merging this one.

Next, we'll create PR for "example" project and improve documentation.