This reorganizes the dEQP build targets to allow for better reuse with
the new KHR test set. It also adds a single new test target called
"angle_deqp_khr_tests" that houses all the new test sets.

The new test targets can be compiled now but cannot yet be executed.
That new functionality will follow in a subsequent CL. Along with test
expectations and integration.

Uses a new template type in the build to conslidate GN customization.

Adds the GLES 2.0 and 3.0 tests for now. We can follow up with
additional work for the GLES 3.1+ tests. Also adds test expectations.

Bug: angleproject:3353
Change-Id: Ib0673e97f679c8aa46e27dfa616845a2014a75fe
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1604070
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>