skia: Add Skia font file data cache

[xiaomings]

Introduce a caching mechanism for Skia font file data.
When enabled via a RefDefault parameter, Skia's file stream
creation uses a global cache, mapping font file paths to their
memory-mapped SkData. This reduces redundant I/O and mapping for
frequently accessed font files.

Bug: 479948202

[github-actions]

🤖 Gemini Suggested Commit Message

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starboard: Add Skia font file data cache

Introduce a caching mechanism for Skia font file data.
When enabled via a RefDefault parameter, Skia's file stream
creation uses a global cache, mapping font file paths to their
memory-mapped SkData. This reduces redundant I/O and mapping for
frequently accessed font files. This feature is specific to the
Starboard platform implementation.

Bug: 479948202

---

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