枚举 WebGLExtension

ANGLE_instanced_arrays EXT_color_buffer_float EXT_color_buffer_half_float EXT_shader_texture_lod EXT_sRGB EXT_texture_filter_anisotropic OES_element_index_uint OES_standard_derivatives OES_texture_float OES_texture_float_linear OES_texture_half_float OES_texture_half_float_linear OES_vertex_array_object WEBGL_compressed_texture_astc WEBGL_compressed_texture_etc WEBGL_compressed_texture_etc1 WEBGL_compressed_texture_pvrtc WEBGL_compressed_texture_s3tc WEBGL_compressed_texture_s3tc_srgb WEBGL_depth_texture