Added floating point formats to glCopyTexImage2D

Added floating point formats to validateColorBufferFormat,
which is used by glCopyTexImage2D, since it was a missing
part of the previously added floating point extensions.

From the extension spec:
https://www.khronos.org/registry/gles/extensions/EXT/EXT_color_buffer_half_float.txt
"9. Should CopyTex[Sub]Image be supported for floating-point formats? [...] Yes."

Change-Id: Ie14d8afd352b004e8a2400cfef16facdeab94e33
Reviewed-on: https://swiftshader-review.googlesource.com/5110
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>