[clang] [clang][NFC] Clean up InitializedEntity booleans. (PR #185335)

[Oliver Hunt via cfe-commits]

https://github.com/ojhunt commented:

In general this looks fine but I'd like @shafik's feedback as well.

My only real question is the reason for not using scoped enums? This is a genuine question outside of just this PR, as enum classes trade off a bunch of convenience in exchange for there tighter type constraints.

I'd certainly prefer enum class as it makes the enumerations read better and avoids accidental bool usage, but I get that it's trade that off against a lot of verbosity and the lack of some basic `if(scopedenumeration)`, etc syntax.

I don't consider this a "must change" consideration, but for instance:

```cpp
enum class MemberInitKind {Default, NonDefault}
```

gives you `MemberInitKind::Default` vs `DefaultMemberInit` which isn't hugely shorter, and seems subjectively better to me, however I recognize it means that in other cases this same pattern causes a lot of verbosity in things like `allowsNRVO()` where you end up with `LocAndNRVO.NRVOMode == NRVOKind::Allowed` under the same scheme.

So again I don't consider this a blocker to the PR, I just want to know if scoped enums were considered and dismissed (partially because I want to do something about some of the annoyances of scoped enums).

https://github.com/llvm/llvm-project/pull/185335