The grammar now accepts type casts, like "(int)x", but that
has to be disambiguated from "(a + b)", needed deeper lookahead
and backing up than what existed so far.
This checkin implements about half of the HLSL intrinsics for a subset of their
entire type support (but a useful subset). The uncommented lines in
TBuiltInParseablesHlsl::identifyBuiltIns shows which are connected.
