- Format table is now initialized using informations from
  https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf.
  Previously, it was setup using gl::GenerateMinimumTextureCaps().

- This CL also adds InitializeTextureDataFunction and LoadFunctionMap to
  mtl::Format. They are needed to properly initialize/convert textures
  with non-normalized formats.

- This CL is prerequisite for integer & floating point format supports.

- New test: DXT1CompressedTextureTest.DXT1Alpha (this test was added
  in the past but was reverted for some reasons).

Bug: angleproject:2634
Change-Id: I5eaad812909a49c4c138d0f65fd21a6a199fcb22
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2332144
Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>