Remove embind from Yoga JavaScript bindings

[NickGerleman]

Summary:
X-link: facebook/yoga#1906

Yoga's JavaScript bindings previously used Emscripten embind to bridge
C++ wrapper classes to JavaScript. This added unnecessary overhead and
complexity: JS calls went through embind → C++ wrapper classes (Node.cpp,
Config.cpp) → Yoga C API, requiring the embind runtime to be bundled into
the WASM output.

This diff removes embind entirely. JavaScript now calls Yoga's C API
directly, with a thin C bridge (wasm_bridge.c, ~140 lines) handling only
what raw C exports cannot:

• Struct returns (YGValue) via a static buffer read through HEAPF32/HEAP32
• Measure/dirtied callbacks via EM_JS dispatching to JS-side Maps

The JS side (wrapAssembly.ts) is rewritten to use classes (NodeImpl,
ConfigImpl) that store a WASM pointer and call C functions directly via
lib._YGFunctionName(). Tree hierarchy (children/parent) is tracked
entirely in JS, matching the pattern used by the Java JNI bindings.

To avoid maintaining a hardcoded EXPORTED_FUNCTIONS list, YG_EXPORT is
extended on Emscripten to include __attribute__((used)) (matching
EMSCRIPTEN_KEEPALIVE). Combined with -fvisibility=hidden and
--export-dynamic, this ensures all public Yoga C API functions are
automatically exported from WASM — no manual list needed. The closure
compiler is retained for JS glue minification.

The public API shape (Yoga, Node, Config types) remains identical.

Bundle size (SINGLE_FILE base64-embedded WASM):

Metric	Before (embind)	After (direct C)	Change
Raw	126,288 B	115,370 B	-8.6%
Gzip	51,042 B	42,764 B	-16.2%

Benchmark results (median of 3 runs):

Benchmark	Before	After	Change
Stack with flex	20ms	8ms	2.5x faster
Align stretch in undefined axis	19ms	5ms	3.8x faster
Nested flex	17ms	4ms	4.3x faster
Huge nested layout	18ms	5ms	3.6x faster

Fixes facebook/yoga#1545

Differential Revision: D95011356

[meta-codesync]

@NickGerleman has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95011356.

[react-native-bot]

This pull request was successfully merged by @NickGerleman in 3cca0d4

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[meta-codesync]

This pull request has been merged in 3cca0d4.