Entry Points: Auto-generate extensions EPs. This is partially complete - it is missing the auto-gen for custom ANGLE and Chromium extensions that aren't present in gl.xml. We can upstream some of these extensions, but will also need to make custom handling for some extensions that are too volatile or under- specced to upstream to Khronos. This also tweaks some of the Context method names to match what the auto-generator expects. It also updates some TexStorage entry points. Also includes a specialized error return value for glTestFenceNV. Also removes the TexImage3DOES entry point which was neither used nor accessible to the application. Bug: angleproject:2263 Change-Id: I3667c22b1b15f84ab4c7dfecb5745aaf73d11e76 Reviewed-on: https://chromium-review.googlesource.com/846420 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org>