Added HelperInvocation to builtin_variables.json, regenerate the codegen
portions of compiler, and plumb support for HelperInvocation through the
rest of the compiler.

Skipping some fails on Android and Swiftshader for this initial change and
will debug/fix those issues in a follow-on.

Bug: angleproject:4110
Change-Id: I781a2782ace84200bc615a2cc26b908a62e2aa26
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1922061
Commit-Queue: Tobin Ehlis <tobine@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>