Support WebAssembly compilation

[SleepySquash]

Synopsis

Flutter brings WebAssembly compilation to its stable branch. However, certain packages don't yet support this.

Solution

Upgrade packages to support building web as a WebAssembly target.

This PR is blocked by the following bugs discovered while testing:

• sqlite3 doesn't support persistence as of now, only in-memory database works. (dart2wasm support simolus3/sqlite3.dart#230)
• HtmlElementView doesn't render properly onto the widget tree due to Flutter unable to render platform views in the WebAssembly currently. (HtmlElementView does render correct scale on wasm flutter/flutter#151104)
• unreachable is thrown when pressing Proceed button of the Introduction modal. ([WASM] Navigator.of(context).pop doesn’t work when passed by reference flutter/flutter#154597)
• Issues with the GalleryPopup: once opened, it will never close, despite animation succeeding.

Additionally it worth noting that only Chrome implements WasmGC required by Flutter to properly render WebAssembly. Firefox, as it seems, has it, but a bug with images being copied every frame makes it unusable. Safari doesn't support WasmGC at all.

Checklist

• Created PR:
  • In draft mode
  • Name contains issue reference
  • Has type and k:: labels applied
• Before review:
  • Documentation is updated (if required)
  • Tests are updated (if required)
  • Changes conform code style
  • CHANGELOG entry is added (if required)
  • FCM (final commit message) is posted or updated
  • Draft mode is removed
• Review is completed and changes are approved
  • FCM (final commit message) is approved
• Before merge:
  • Milestone is set
  • PR's name and description are correct and up-to-date
  • All temporary labels are removed

[SleepySquash]

Despite drift fixing the issue, we still await the new dart2wasm compiler (comes with a new Dart SDK), because there're a lot of casting issues when doing INSERT/DELETE/SELECT, etc:

[tyranron]

@SleepySquash could you add to the PR description the relative tracking links for each issue?

[SleepySquash]

Update: latest drift persists data with unsafe IndexedDB, works like a charm.

[SleepySquash]

Latest master branch of Flutter fixes unreachable and GalleryPopup related issues. The only thing left is fixing the HtmlElementViews - while their positioning is already fixed, their clipping is still incorrectly displayed. E.g. if HtmlElementVIew is not positioned in the left top corner, then it'll be clipped.