mImage2DUniforms was not saved with the program binary causing shaders with
images to fail compilation when loaded from binary.

BUG: angleproject:4519
BUG: b:152292873
Change-Id: I51581031ae1f9d4b4d986057ef3f876d809c7f24
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2124587Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Courtney Goeltzenleuchter <courtneygo@google.com>