If there is a "constant" enum argument to a synthesized enum comparison, we can always inline it, because most of it will be constant folded anyway.
This ensures the compiler is not creating terrible code for very simple enum comparisons, like
```
if someEnum == .someCase {
...
}
```
rdar://85677499
Optimize (the very inefficient) RawRepresentable comparison function call to a simple compare of enum tags.
For example,
```
enum E: String {
case a, b, c
}
```
is compared by getting the raw values of both operands and doing a string compare.
This peephole optimizations replaces the call to such a comparison function with a direct compare of the enum tags, which boils down to a single integer comparison instruction.
rdar://151788987
