This will more easily allow us to extend our implementation to make a
NULL or "stub" set of bindings. It also exposes a lot more function
permutations via extension variations.

It might improve the loading speed for bindings obtained via
extensions. Instead of generating a list every time an extension is
checked, we use a single std::set for a fast query. However because
more extensions are checked for more entry points, it might not make
a huge difference.

This also fixes an issue where the "real" ANGLE GL headers were being
propagated to the entry point dispatch table definitions, instead of
being in a totally isolated file. This patch adds the missing typedefs
to our proxy headers.

It also fixes the naming of a few entry points which was inconsistent
with the spec. It also makes an XML adjustment to GL_NV_path_rendering
to accomodate a hole in the spec where glLoadMatrixfEXT was not ever
defined in OpenGL ES. A spec oddity with the TexStorage extension is
not resolved - in this case, some methods are only exposed if other
extensions are present, but this information is missing from gl.xml.

BUG=angleproject:2188

Change-Id: I0fd61dd32de6fadd55fa6bd79295833392d51104
Reviewed-on: https://chromium-review.googlesource.com/726949
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>