Make the debug interface a GrGLTestInterface subclass.

The debug interface subsumes the GrDebugGL singleton which allows multiple instances.

Fixes a few issues that existed before this CL (pack alignment wasn't tracked or respected, and we weren't initializing a texture id to 0 in one GM). Apparently this is not currently run on the bots.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1812323002

Review URL: https://codereview.chromium.org/1812323002
9 files changed