Rename variables named `input` in test files.

`input` is a reserved word in GLSL. http://screen/85m4iRwvJRadKbV

Change-Id: Iffc0a47d916a2419a27767902c839e09bfa7fe26
Bug: skia:11115
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/454736
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
120 files changed