Verify texImage2D and texSubImage2D code paths taking a sub-rectangle of a canvas (ALPHA/ALPHA/UNSIGNED_BYTE)

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

TEST COMPLETE: 1 PASS, 0 FAIL

Test only applies to WebGL 2.0
PASS successfullyParsed is true

TEST COMPLETE