Add support for creating images with custom colorspace.

Bug: angleproject:3756
Tests: angle_end2end_tests --gtest_filter=ImageTest*
Change-Id: I9c332c012541c094728d9d9bde7add4189084a33
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2104088Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>