Add test of gl_VertexID and gl_InstanceID.

Includes details in new test about both state-of-specification, and known errata.

Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1779800

Author: kdashg

sdk/tests/conformance2/rendering/00_test_list.txt

@@ -11,6 +11,7 @@ blitframebuffer-size-overflow.html
 --min-version 2.0.1 blitframebuffer-stencil-only.html
 blitframebuffer-test.html
 --min-version 2.0.1 blitframebuffer-unaffected-by-colormask.html
+--min-version 2.0.1 builtin-vert-attribs.html
 canvas-resizing-with-pbo-bound.html
 --min-version 2.0.1 clearbuffer-sub-source.html
 --min-version 2.0.1 clearbufferfv-with-alpha-false.html