Use compressed internal format as 'format' in tables.
Use compressed internal format as 'format' in tables.

Previously we would store the unsized 'base' format as the internal
format. For instance for GL_COMPRESSED_RGB_S3TC_DXT1_EXT we would store
GL_RGB. With the new spec validation for TexSubImage it becomes clearer
to store the internal format of the compressed texture as the 'format'.

Bug: angleproject:3170
Change-Id: I7446418896eabd3d4f143e9cae4976889b973674
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1553379
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Reviewed-by: Tim Van Patten <c7814369a8d3d5671c484acc7b3215f1bf4221be@google.com>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle