Better dual ESM/CJS support, tsconfig module now Node16, improved pnpm support

[huntj88]

• Update Module and ModuleResolution to Node16 in tsconfig.
  • This is what FluidFramework is doing for their default tsconfig's
  • FF expects that all customers update TS configuration to use Node16+ compatible resolution.
    • example: "module": "Node16" + "moduleResolution": "Node16"
    • For apps, they often want "module": "ESNext" + "moduleResolution": "Bundler"
• Add .js extensions throughout code.
• export package.json override on CJS builds for {type: commonjs}
• Added resolution support for @microsoft/live-share/internal for Node10.
  • ESM only for Node10, CJS not supported. This matches FF.
• update live-share-acs, live-share-canvas, live-share-react to ship CJS and ESM builds.
• update live-share index to not have a root index, just index.public.ts and index.internal.ts
• updated dependencies and peerDependencies.
  • Improved pnpm support [Feature Request]: Clean support for strict dependency managers (e.g., pnpm default) #745
  • Moved some dev dependencies to direct dependencies
• Added a pnpm project, and a CI check to ensure that Live Share works and is simple to use with pnpm

[ryanbliss]

LGTM