OpenGL2: Disable the VAO cache by default

The VAO surface cache uses glBufferSubData and triggers a very slow
path in some GLES implementations. Specifically I have observed 10x
frame times under Emscripten with ANGLE/Metal on macOS and with Mali
on Android.

Co-authored-by: Zack Middleton <zack@cloemail.com>
Co-authored-by: WofWca <wofwca@protonmail.com>

code/renderergl2/tr_surface.c

@@ -409,6 +409,9 @@ static qboolean RB_SurfaceVaoCached(int numVerts, srfVert_t *verts, int numIndex
 	qboolean recycleIndexBuffer = qfalse;
 	qboolean endSurface = qfalse;
 
+	if (!r_vaoCache->integer)
+		return qfalse;
+
 	if (!(!ShaderRequiresCPUDeforms(tess.shader) && !tess.shader->isSky && !tess.shader->isPortal))
 		return qfalse;