Capture/Replay: Handle default uniforms during MEC During mid-execution capture, when processing uniforms for a program, capture their values and repopulate during replay. Test: Temple Run MEC capture and replay Bug: b/152512564 Bug: angleproject:3662 Change-Id: If84711ead144b7c88710e6b12d0968e80e263c69 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2155489 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>