This is to be able to perform validation inside TranslatorVulkan, even
if it's through ASSERTs.

Additionally, every transformation is changed such that they do their
validation themselves.  TIntermTraverser::updateTree() performs the
validation, which indirectly validates many of three tree
transformations.  Some of the more ancient transformations that don't
use this function directly call TCompiler::validateAST.

Bug: angleproject:2733
Change-Id: Ie4af029d34e053c5ad1dc8c2c2568eecd625d344
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1761149Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>