message: WebGL: fix isTextureFormatSupported for ETC2 formats.
  It was assumed that ETC2 is supported on all ES3 devices, but WebGL on
  desktop machines does not support ETC2.
  Note that WebGL has its own special extension strings for compressed
  textures.
diff: @@ -306,7 +306,9 @@ void OpenGLContext::initExtensionsGLES() noexcept {
  ext.EXT_multisampled_render_to_texture = exts.has("GL_EXT_multisampled_render_to_texture"sv);
  ext.EXT_multisampled_render_to_texture2 = exts.has("GL_EXT_multisampled_render_to_texture2"sv);
  ext.EXT_shader_framebuffer_fetch = exts.has("GL_EXT_shader_framebuffer_fetch"sv);
  +#if !defined(__EMSCRIPTEN__)
  ext.EXT_texture_compression_etc2 = true;
  +#endif
  ext.EXT_texture_filter_anisotropic = exts.has("GL_EXT_texture_filter_anisotropic"sv);
  ext.GOOGLE_cpp_style_line_directive = exts.has("GL_GOOGLE_cpp_style_line_directive"sv);
  ext.KHR_debug = exts.has("GL_KHR_debug"sv);
  