glsl: Classify "layout" like other identifiers.

glsl: Classify "layout" like other identifiers.

When "layout" isn't being lexed as LAYOUT_TOK, we should treat it like
an ordinary identifier.  This means we need to classify it to determine
whether we should return IDENTIFIER, TYPE_IDENTIFIER, or NEW_IDENTIFIER.

Fixes the WebGL conformance test "shader-with-non-reserved-words."

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=64087
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org