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

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