docs(rfcs): create packaging for npm registry (#19066)

* docs(rfcs): create packaging for npm registry

Co-authored-by: Oleksandr Fediashov <alexander.mcgarret@gmail.com>

rfcs/build-system/03-packaging-for-npm.md

@@ -0,0 +1,202 @@
+# RFC: Packaging for npm registry
+
+---
+
+_List contributors to the proposal here: @hotell_
+
+## Summary
+
+> #### 💡 NOTE: This proposal/guide applies only for vNext packages and libraries using new DX
+
+## Problem statement
+
+We ship lot of unnecessary stuff to our consumers:
+
+- story files
+- source files
+- various configurations and metadata
+- others...
+
+What we ship is driven by our current npm package setup, which looks like following:
+
+**`<package>/.npmignore`**
+
+```
+*.api.json
+*.config.js
+*.log
+*.nuspec
+*.test.*
+*.yml
+.editorconfig
+.eslintrc*
+.eslintcache
+.gitattributes
+.gitignore
+.vscode
+coverage
+dist/storybook
+dist/*.stats.html
+dist/*.stats.json
+dist/demo
+fabric-test*
+gulpfile.js
+images
+index.html
+jsconfig.json
+node_modules
+results
+src/**/*
+!src/**/examples/*.tsx
+!src/**/docs/**/*.md
+!src/**/*.types.ts
+temp
+tsconfig.json
+tsd.json
+tslint.json
+typings
+visualtests
+```
+
+> **NOTE:** data was acquired by running `npm pack --dry-run` in `packages/react-text`
+
+**Packaged output:**
+
+```
+=== Tarball Details ===
+name:          @fluentui/react-text
+version:       9.0.0-alpha.0
+package size:  564.2 kB
+unpacked size: 2.2 MB
+total files:   1008
+```
+
+With manually removed `.cache` folder:
+
+```
+=== Tarball Details ===
+name:          @fluentui/react-text
+version:       9.0.0-alpha.0
+package size:  31.1 kB
+unpacked size: 263.9 kB
+total files:   518
+```
+
+## Detailed Design or Proposal
+
+> **💡 NOTE:** This proposal/guide applies only for vNext packages and libraries using new DX
+
+This is a living document that will describe various proposals that all aim to improve following common goals:
+
+- packaging size to npm registry
+- faster install/over the wire transfer/less bytes
+- faster packages consumption/processing by consumers
+- better security for consumers
+- better tree-shaking capabilities
+
+### 1. `.npmignore` cleanup
+
+**`<package>/.npmignore`**
+
+```sh
+.cache/
+.storybook/
+.vscode/
+coverage/
+src/
+bundle-size/
+config/
+temp/
+e2e/
+node_modules/
+__fixtures__
+__tests__
+
+*.log
+*.yml
+*.test.*
+*.spec.*
+*.stories.*
+*.api.json
+
+# config files
+.git*
+*rc.*
+*config.*
+.eslint*
+.editorconfig
+.prettierignore
+```
+
+> **NOTE:** data was acquired by running `npm pack --dry-run` in `packages/react-text`
+
+**Packaged output:**
+
+```
+=== Tarball Details ===
+name:          @fluentui/react-text
+version:       9.0.0-alpha.0
+package size:  24.7 kB
+unpacked size: 172.8 kB
+total files:   250
+```
+
+#### Pros
+
+This approach significantly improves our current situation:
+
+- simpler `npmignore` configuration / better maintenance
+- only implementation is being shipped (no tests, stories)
+- **52% less files**
+- **21% smaller packed package size**
+
+#### Cons
+
+- none
+
+#### Discarded Solutions
+
+- using `"files"` withing `package.json`
+  - doesn't support exclusion patterns
+  - non explicit for human (if `files` property is used, some files will be automatically and always shipped)
+  - 2 sources of "truth" (`.npmignore` and `files`)
+
+### 2. shipping only type definition rollup
+
+> **NOTE:** to make this RFC more focused this will be covered in followup PR's if needed
+
+#### Pros
+
+- TBA
+
+#### Cons
+
+- TBA
+
+### 3. shipping only rollup-ed(bundled) implementation files
+
+> **NOTE:** to make this RFC more focused this will be covered in followup PR's if needed
+
+#### Pros
+
+- TBA
+
+#### Cons
+
+- TBA
+
+### 4. package.json post-processing
+
+> **NOTE:** to make this RFC more focused this will be covered in followup PR's if needed
+
+#### Pros
+
+- TBA
+
+#### Cons
+
+- TBA
+
+## Open Issues
+
+- https://github.com/microsoft/fluentui/issues/19042