This warning verifies we don't give variables names that shadow
fields. This is another good warning to enable that Skia requires.
This CL also fixes a small number of points in code that used this
bad pattern. We have to disable the warning for Glslang for now.

Bug: angleproject:4046
Change-Id: I072a686e3023b60cfafa778525fe712ce1fb5a50
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1877476Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>