Bug 250558

How to reproduce:
1. Create a new Untiy WebGL project with an empty scene, 
2. Set graphic api to WebGL2，
3. Set WASM initial memory to a large size (by adding "-s TOTAL_MEMORY=768MB" to PlayerSettings.WebGL.emscriptenArgs)
4. Build and load with Safari on iPhone12 with iOS16,
5. Safari report error when loading.

Rootcause:
Unity called texSubImage2D during initialization, Safari report error when invoking this api due to insufficient memory.
But that texture is 4*4 RGBA UNSIGNED_BYTE, should not cause any memory pressure.
When looking into WebGL2RenderingContext::texSubImage2D in WebKit source code, we found:
In WebGLRenderingContextBase::texImageArrayBufferViewHelper, variable 'data' created by WebGLRenderingContextBase::validateTexFuncData has incorrect value.
data.m_bufSize ought to be pixel data length, but acturally assigned as arrayBuffer(whole WASM memory) length - pixel data offset, which is much more larger.
Then later in IPC::Encoder::encodeFixedLengthData, encoder buffer will grow by this large size and lead to memory issue.