Trace Tests: Load trace list from JSON file. Instead of using the auto-generated enum for the trace list, load directly from restricted_traces.json. This will lead to more CLs that entirely remove the auto-generated code from the trace tests. Bug: angleproject:5133 Change-Id: I6515624a2145319d097b43085741cf9c48f1792e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3140217 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>