Explicit control in tools of ANGLE frontend and backend

Explicit control in tools of ANGLE frontend and backend

Update the ANGLE test GL context, GrContextFactory, and config parsing to allow explicit control of ANGLE front/backend.

This will allow us to explicitly test ES2 vs ES3 interfaces to ANGLE as well as D3D9, D3D11, and OpenGL backends.

Also makes the angle api types valid in all builds (but will just fail when SK_ANGLE=1 or not on windows for the d3d backends).

BUG=skia:5804
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2381033002

CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Win-MSVC-ShuttleC-GPU-GTX960-x86_64-Debug-ANGLE-Trybot

Review-Url: https://codereview.chromium.org/2381033002