Remove embind from Yoga JavaScript bindings (facebook#55864)

Summary:
Pull Request resolved: facebook#55864

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.

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

Changelog: [Internal]

Reviewed By: elicwhite

Differential Revision: D95011356

fbshipit-source-id: a936a9e6705aebe66bf7515ccd67cdc0f55ccae2

Author: NickGerleman

packages/react-native/ReactCommon/yoga/yoga/YGMacros.h

@@ -29,6 +29,8 @@
 
 #ifdef _WINDLL
 #define YG_EXPORT __declspec(dllexport)
+#elif defined(__EMSCRIPTEN__)
+#define YG_EXPORT __attribute__((visibility("default"), used))
 #elif !defined(_MSC_VER)
 #define YG_EXPORT __attribute__((visibility("default")))
 #else