Scanner: Many int64 fixes, including performance.

- partially addresses #1209 and #1187
- only query 64-bit extension on seeing use of a 64-bit literal
  (was doing it for every single token)
- correct HLSL acceptance of 64-bit literal syntax (still an int though)
- error on overflow of 32-bit literal type

Test/baseResults/preprocessor.simple.vert.out

@@ -25,6 +25,6 @@ int main(){
   == !=
   & ^ | && ^^ || ? :
   += -= *= /= %= <<= >>= &= |= ^=
-  1.2 2E10 5u - 5 lf
+  1.2 2E10 5u - 5l f
 }