This extension is always needed for replay, and it should always
be enabled. By adding the extension using esOnlyExtension it is
no longer marked as requestable and WebGL compatibility will no
longer disable the extension.

Bug: angleproject:5851
Change-Id: I11c8f684b3bfe76c219a9210df0a2c5cccb706f3
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2853583
Commit-Queue: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>