In both the ESSL 1.00 & 3.00 specifications having an extension directive
after a pre-processor token is an error. Merging those two enum cases to
be a single case. WebGL is handled as a separate warning case for any
shader version before 3.00.

Also this change now correctly marks 1.00 shaders that break this rule
to be invalid so the ExtensionAfterNonPreProcessorTokenESSL1 test no
longer expects handleExtension() to be called.

BUG=chromium:971660

Change-Id: I37b10cc0fb3a0efd6200a478171e005a96478255
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1661395Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>