Refactor `BuildMetadata` to be simpler

[daohoangson]

Goal: merge BuildMetadata into BuildTree.

[github-actions[bot]]

Demo app

63e1f70b671be8ad22a0ae22b84d29ff02341b8a APKs:

• app-armeabi-v7a-release.apk
• app-arm64-v8a-release.apk
• app-x86_64-release.apk
• Debug APK via https://appetize.io

Web build has been deployed to https://example-aycy4d65t-flutter-widget-from-html.vercel.app. Quick links:

• supported/tags.html
• Hello World
• Hello World (core)
• Wordpress

[codecov[bot]]

Codecov Report

Patch coverage: 99.74% and project coverage change: -0.09 :warning:

Comparison is base (04054df) 98.90% compared to head (63e1f70) 98.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #649      +/-   ##
==========================================
- Coverage   98.90%   98.81%   -0.09%     
==========================================
  Files          62       63       +1     
  Lines        3917     3890      -27     
==========================================
- Hits         3874     3844      -30     
- Misses         43       46       +3     

Impacted Files	Coverage Δ
packages/core/lib/src/core_data.dart	100.00% <ø> (ø)
packages/core/lib/src/modes/render_mode.dart	100.00% <ø> (ø)
...ackages/core/lib/src/internal/margin_vertical.dart	87.50% <80.00%> (-12.50%)	:arrow_down:
...ackages/fwfh_webview/lib/src/web_view_factory.dart	86.48% <88.23%> (-3.26%)	:arrow_down:
packages/core/lib/src/core_helpers.dart	100.00% <100.00%> (ø)
packages/core/lib/src/core_html_widget.dart	100.00% <100.00%> (ø)
packages/core/lib/src/core_widget_factory.dart	100.00% <100.00%> (ø)
packages/core/lib/src/data/build_bits.dart	100.00% <100.00%> (ø)
packages/core/lib/src/data/css.dart	100.00% <100.00%> (ø)
packages/core/lib/src/data/html_style.dart	100.00% <100.00%> (ø)
... and 33 more

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