Extend preinitialization interpreter

This is enough to support preinitializing:

```csharp
static readonly SearchValues<char> s_searchValues = SearchValues.Create("Lol");
```

Things that I had to add:

* Support for `typeof(T) == typeof(Bar)` (this will be useful later, we'll eventually be able to also freeze these).
* Support static interface method calls
* Constrained method calls on valuetypes
* More `ReadOnlySpan` construction patterns, `.Length`
* More indirect load/store support

Resolves dotnet#78681.