NativeEngine: implement updateTextureData (re-enables Test updateTextureData)

[bkaradzic-microsoft]

Paired engine PR: BabylonJS/Babylon.js#18566

What

Implements updateTextureData on the native engine so partial (sub-rectangle) texture updates work;
previously it threw "not implemented". Pairs with the Babylon.js change that also stops the native
engine reporting engine.name === "WebGL" (that masquerade made engine.name-gated WebGL _gl
access run on native and crash with TEXTURE_2D undefined).

Changes

• Plugins/NativeEngine/Source/NativeEngine.cpp / .h: add NativeEngine::UpdateTextureData, which
  uploads the requested sub-rectangle via bgfx::updateTexture2D (Texture::Update2D). It validates
  the JS-controlled rectangle against the mip-level extents, sizes the copy with
  bgfx::calcTextureSize (bgfx is always linked, unlike bimg, so this also works in builds without
  image loading), and mirrors the vertical flip the base texture upload applies so the sub-rectangle
  lines up on top-left-origin backends (e.g. D3D11).
• Apps/Playground/Scripts/config.json: re-enable "Test updateTextureData".

CI

The validation suite uses the published babylonjs npm, which does not yet contain the paired JS
overrides, so the re-enabled test stays red until a babylonjs release with the Babylon.js change
ships and the dependency is bumped here. Draft until then.

Verified locally

Built against a local babylon.max.js with the paired change: the re-enabled test passes (stable
across repeated runs); no regressions in other texture / raw-texture tests.

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Related PRs & landing order

• Babylon.js (engine / TS): [Native] Report engine.name "Native" and implement updateTextureData Babylon.js#18566
• BabylonNative (C++ engine + test re-enable): NativeEngine: implement updateTextureData (re-enables Test updateTextureData) #1751

Co-dependent; land in this order:

1. Babylon.js #18566 first — adds the engine.name = "Native" + updateTextureData TS overrides; no WebGL behavior change.
2. A babylonjs npm release ships that TS change.
3. BabylonNative NativeEngine: implement updateTextureData (re-enables Test updateTextureData) #1751 last — bumps the bundled babylonjs and re-enables the Test updateTextureData validation test, which only passes once the paired JS is present in the bundled engine.