Support shifts and a few other ops in front-end constant folding (#1027)

The set of supported operations in front-end constant folding was very limited: `+`, `-`, `*`, `/`, and `%`.
This meant that enum declarations like:

```
enum MyBits
{
    A = 1 << 0,
    B = 1 << 1,
    C = A | C,
}
```

would fail to compile, with a claim that the expressions like `1 << 0` aren't compile-time constants.

This change adds `<<`, `>>`, `&`, `|`, and `^` to the list of integer operations we will cosntant-fold in the front-end. It also changes one of the declarations in the existing test case for `enum`s to use the added functionality.

Note that this change does *not* address the more deep-seated problems with our approach to constant-folding in the front-end. It does not change the constant folding to rely on IR machinery, or to allow for more general `constexpr` functions, and it does not address the fact that constant-folding is currently applied without paying attention to the type (and thus precision) of the original expression.

0 files changed, 0 insertions, 0 deletions