Improve dynamic numVertices change performance for vertexBuffer

[AlexAPPi]

There is currently no way to dynamically quickly change the size of the storage area, but after removing webgl1 support, you can use:

https://registry.khronos.org/webgl/specs/latest/2.0/

  undefined bufferSubData(GLenum target, GLintptr dstByteOffset, [AllowShared] ArrayBufferView srcData,
                          unsigned long long srcOffset, optional GLuint length = 0);

https://github.com/playcanvas/engine/blob/main/src/platform/graphics/webgpu/webgpu-buffer.js#L91
https://github.com/playcanvas/engine/blob/main/src/platform/graphics/webgl/webgl-buffer.js#L49

Tested successfully: https://github.com/AlexAPPi/playcanvas-terrain-system/blob/main/src/ScriptHelpers/TerrainPatchesInstancing.mts#L93