Add restrictions for ES2 TexSubImage for format

  Validation errors for TexSubImage calls are similar to TexImage,
although with the current texture's internal format replacing the
explicit internal format arg. One of the validation conditions is
a valid combination of the internal format, format, and type args
as per the respective spec. However, currently no comprehensive method
to check format combinations for TexSubImage calls exists for ES2
(included in ValidateES2TexImageParameters()), especially since in
some extensions, it is allowed to use internal formats not equal to
format in the underlying glTexImage*() calls.

This causes TexSubImage to allow illegal combinations (for example,
for RGBA/UBYTE, which is effectively RGBA8, it allows USHORT_4_4_4_4).
This leads to crashes (due to UNREACHABLE()) on debug mode, and ignored
silently on release mode.

This change tightens the restrictions to prevent such scenarios.

* Used ValidES3FormatCombination(), which is used to validate format
  and type combinations for glTexSubImage*() calls.

  * (For some core ES2 formats with new combinations, the required
    extensions are checked as well.)

  * It takes the corresponding internal format info of the texture
    and checks if the format and type args should be accepted with
    respect to the sized internal format.

  * For most cases, the format and type of the texture update must
    match those used in the original texture init. However, some
    formats may accept additional combinations, which are also taken
    into account.

* Added basic tests to Texture2DTest checking texture init and update
  using various formats.

* Added the remaining GLColorRGB constants.

Bug: chromium:516824665
Change-Id: Ia83a334bd66c4a957c7c6822dc08f8d9b025574a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7920728
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Amirali Abdolrashidi <abdolrashidi@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>