GL_CHROMIUM_color_buffer_float_rgba extension support

GL_CHROMIUM_color_buffer_float_rgba extension support

GL_CHROMIUM_color_buffer_float_rgba (OpenGL ES 2.0) is a subset of
GL_EXT_color_buffer_float (OpenGL ES 3.0), which SwiftShader already
supports.

Fixes 1 webgl conformance tests:
conformance/extensions/oes-texture-float.html

Change-Id: Ic1451187db219af74ba41fa7634bd5bcb6fb0b44
Reviewed-on: https://swiftshader-review.googlesource.com/16470
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>