HLSL adds a unique id suffix to user defined variable and these numbers
are currently hardcoded in tests. It could easily fail if new tokens are
added to angle builtin variables.

Introduce C++11 regex feature into the foundInHLSLCode to avoid over
strict tests.

Bug: angleproject:3551
Change-Id: Ia3052afec667a7ac11198be31b5c1d03c856a723
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1670581Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Shrek Shao <shrekshao@google.com>