[lldb] Unify type name matching in FormattersContainer

[lldb] Unify type name matching in FormattersContainer

Summary:

FormattersContainer stores LLDB's formatters. It's implemented as a templated
map-like data structures that supports any kind of value type and only allows
ConstString and RegularExpression as the key types. The keys are used for
matching type names (e.g., the ConstString key `std::vector` matches the type
with the same name while RegularExpression keys match any type where the
RegularExpression instance matches).

The fact that a single FormattersContainer can only match either by string
comparison or regex matching (depending on the KeyType) causes us to always have
two FormatterContainer instances in all the formatting code. This also leads to
us having every type name matching logic in LLDB twice. For example,
TypeCategory has to implement every method twice (one string matching one, one
regex matching one).

This patch changes FormattersContainer to instead have a single `TypeMatcher`
key that wraps the logic for string-based and regex-based type matching and is
now the only possible KeyType for the FormattersContainer. This means that a
single FormattersContainer can now match types with both regex and string
comparison.

To summarize the changes in this patch:
* Remove all the `*_Impl` methods from `FormattersContainer`
* Instead call the FormatMap functions from `FormattersContainer` with a
  `TypeMatcher` type that does the respective matching.
* Replace `ConstString` with `TypeMatcher` in the few places that directly
  interact with `FormattersContainer`.

I'm working on some follow up patches that I split up because they deserve their
own review:

* Unify FormatMap and FormattersContainer (they are nearly identical now).
* Delete the duplicated half of all the type matching code that can now use one
  interface.
* Propagate TypeMatcher through all the formatter code interfaces instead of
  always offering two functions for everything.

There is one ugly design part that I couldn't get rid of yet and that is that we
have to support getting back the string used to construct a `TypeMatcher` later
on. The reason for this is that LLDB only supports referencing existing type
matchers by just typing their respective input string again (without even
supplying if it's a regex or not).

Reviewers: davide, mib

Reviewed By: mib

Subscribers: mgorny, JDevlieghere

Differential Revision: https://reviews.llvm.org/D84151