Cleanup POD struct usage to make them more consistent In recent months, I have made many CLs to wrap various data structures into a trivially copy-able struct. Some of them uses different terminology. This CL replaces all of these to use a consistent name "pod" in the struct, and "mPod" in a class. This CL also turns ActiveVariable methods into macros to remove the code duplication. This CL also moves ProgramInput/ProgramOutput struct implementations from Program.cpp to ProgramExecutable.cpp Bug: b/275102061 Change-Id: Ia2a4210a9ea633f3d323bebe674ee74f8b90b363 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4877335 Commit-Queue: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Roman Lavrov <romanl@google.com>