Add contextType() accessor to test contexts.

This will be used in a followup to handle SkSL test filtering.

Change-Id: Ia0886035aa24def8f9455d8b106bf79d24483b34
Bug: b/40044139
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/757216
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
7 files changed