These tests are frequently cloned to make new tests, and so it's good
to do a more-global refactor so that these and future tests will use
RAII.

Bug: angleproject:4947
Change-Id: I2973e70ee075629965b18c685793975537e96b6c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2372627Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Ian Elliott <ianelliott@google.com>