SPV: RelaxedPrecision: Generalize fix #2293 to cover more operations.

This simplifies and enforces use of precision in many more places,
to help avoid accidental loss of RelaxedPrecision through intermediate
operations. Known fixes are:
- ?:
- function return values with mis-matched precision
- precision of function return values when a copy was needed to fix types

Test/spv.precision.frag

@@ -57,4 +57,6 @@ void main()
     
     mediumfout *= s.a;
     mediumfout *= s.b;
+
+    mediumfout = ((mediumfin * mediumfin > 4.2) ? 2.0 * mediumfout : 3.0 * mediumfout);
 }