This is a first step towards auto-generating more EGL code. It
includes format handling for all the EGL parameter types, type
reinterpretation for EGL types using the "packed enum" handling,
and code refactoring to support the new consistent validation
entry point pattern.

Bug: angleproject:2621
Change-Id: I2740e82928db311aa934825cbe74bd75bf49c33c
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2552976
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Cody Northrop <cnorthrop@google.com>