mesa/tests: Sanity check the ES2 dispatch table

mesa/tests: Sanity check the ES2 dispatch table

This test is only built when shared-glapi is used.  Because of changes
elsewhere in the tree that were necessary to make shared-glapi work
correct with GLX, it's not feasible to make the test function both ways.

The list of expected functions originally came from the functions set by
api_exec_es2.c.  This file no longer exists in Mesa (but api_exec_es1.c
is still generated).  It was the generated file that configured the
dispatch table for ES2 contexts.  This test verifies that all of the
functions set by the old api_exec_es2.c (with the recent addition of VAO
functions) are set in the dispatch table and everything else is a NOP.

When adding ES2 (or ES3) extensions that add new functions, this test
will need to be modified to expect dispatch functions for the new
extension functions.

v2: Expect VAO functions be non-NOP.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>