This is in preparatino for auto-generating the EGL validation header.
The auto-generation script will force multiple parameters to const.

Bug: angleproject:2621
Change-Id: I04e442c6ff118fd7c296341f12f442901f6fb8c0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2552979Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>