Support wide bitvector types (>64 bits) in cpp transpiler for enums

**Describe the bug**
DSLX enums which are wider than 64 bits are truncated down to 64 bits in the cpp_transpiler

**To Reproduce**

Run cpp transpiler with:

```
enum MyUnsupportedWideEnum : uN[555] {
A = 0,
B = sN[555]:-1 as uN[555],
}
```

**Expected behavior**
Some way of encoding B and the type as 555 bits

**Current Behavior**
```
enum class MyUnsupportedWideEnum: int64_t {...}
```

See https://github.com/google/xls/issues/1135