gles2: support for GL_EXT_occlusion_query_boolean

gles2: support for GL_EXT_occlusion_query_boolean

Following test checking entrypoints passes:
   dEQP-EGL.functional.get_proc_address.extension.gl_ext_occlusion_query_boolean

Piglit test 'ext_occlusion_query_boolean-any-samples' passes with these changes.

No changes/regression observed in WebGL occlusion tests or Intel CI.

v2: add es2="2.0" for glapi entrypoints, clean up xml
    dispatch_sanity changes (fix 'make check')

Signed-off-by: Harish Krupo <harish.krupo.kps@intel.com>
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>