[web] Cover Skwasm font loading from Dart and JavaScript byte views #194217

Skwasm font loading accepts a Uint8List, which may be a view into a larger buffer or backed by a JavaScript Uint8Array. Focused engine tests should preserve this behavior when the font-data copy path changes.

Proposed coverage:

• A Dart-allocated Uint8List and JSUint8Array.withLength(...).toDart.
• A font view starting at byte offset 0 and at byte offset 13.

Each case places a valid Ahem font into a larger buffer, takes a Uint8List.sublistView of the font bytes, verifies that SkwasmFontCollection.loadFontFromBytes succeeds, and checks that the entire source buffer remains unchanged, including sentinel bytes outside the view.

All four cases already pass at b314ad53146b1bde55b60197a35183fb530aac0a in the chrome-coi-dart2wasm-skwasm-skwasm suite. This tracks additional coverage for existing behavior, requires no production change, and makes no performance claim.