[vector_graphics_compiler] Ignore unrecognized font-weight values

[Yusufihsangorgel]

Fixes flutter/flutter#186933

SvgParser.parseFontWeight throws on any value outside the recognized CSS
keywords and numeric weights. That makes the whole SVG fail to compile for
non-standard values such as font-weight="regular".

This change treats an unrecognized value as an invalid declaration: it emits a
warning and returns no parsed value, so normal style inheritance still applies.
An unstyled root therefore keeps the initial normal weight, while an invalid
child declaration no longer overrides a bold parent. Strict
warningsAsErrors builds continue to throw.

Tests cover an unrecognized root value, inheritance from a bold parent, and the
warnings-as-errors path. flutter analyze and the full 333-test
vector_graphics_compiler suite pass locally.

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[gemini-code-assist]

Code Review

This pull request updates the SVG parser in vector_graphics_compiler to accept the non-standard font-weight 'regular' value as an alias for 'normal'. It also changes the behavior for unrecognized font-weight values to print a warning and fall back to normal weight instead of throwing a StateError, unless warnings are configured as errors. Relevant tests, changelog entries, and version bumps are included. There are no review comments, and I have no feedback to provide.

[stuartmorgan-g]

For engine team reviewers: I left a comment on the issue; it's not clear to me that adding explicit handling of the non-standard value is actually something we want.

[Yusufihsangorgel]

Agreed — (C) is the right call. An invalid font-weight is dropped at parse time per CSS error handling, so the element just keeps the default (normal); following that is cleaner than special-casing regular. I've updated the PR to remove the explicit alias and keep only the generic fallback: an unrecognized value resolves to normalFontWeight with a warning, and still throws under warningsAsErrors so strict builds are unaffected. That covers the reported VectSharp output as a byproduct of following the spec, without blessing a non-standard keyword.

[andywolff]

Looks good to me. I agree with @stuartmorgan-g 's comment suggesting option C, thanks for updating to that approach.

[andywolff]

I think the CI failure is likely flutter/flutter#190084 and not caused by this PR

[Yusufihsangorgel]

flutter/flutter#190084 closed this morning. The two failed android_build_all_packages runs predate the fix, so a presubmit re-run should come back green. Happy to rebase to re-trigger if that's easier.

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