[AST] Add dump() method to TypeLoc (#65484)

The ability to dump AST nodes is important to ad-hoc debugging, and
the fact this doesn't work with TypeLoc nodes is an obvious missing
feature in e.g. clang-query (`set output dump` simply does nothing).

Having TypeLoc::dump(), and enabling DynTypedNode::dump() for such nodes
seems like a clear win.

It looks like this:
```
int main(int argc, char **argv);

FunctionProtoTypeLoc <test.cc:3:1, col:31> 'int (int, char **)' cdecl
|-ParmVarDecl 0x30071a8 <col:10, col:14> col:14 argc 'int'
| `-BuiltinTypeLoc <col:10> 'int'
|-ParmVarDecl 0x3007250 <col:20, col:27> col:27 argv 'char **'
| `-PointerTypeLoc <col:20, col:26> 'char **'
|   `-PointerTypeLoc <col:20, col:25> 'char *'
|     `-BuiltinTypeLoc <col:20> 'char'
`-BuiltinTypeLoc <col:1> 'int'
```

It dumps the lexically nested tree of type locs.
This often looks similar to how types are dumped, but unlike types
we don't look at desugaring e.g. typedefs, as their underlying types
are not lexically spelled here.

---

Less clear is exactly when to include these nodes in existing text AST
dumps rooted at (TranslationUnit)Decls.
These already omit supported nodes sometimes, e.g. NestedNameSpecifiers
are often mentioned but not recursively dumped.

TypeLocs are a more extreme case: they're ~always more verbose
than the current AST dump.
So this patch punts on that, TypeLocs are only ever printed recursively
as part of a TypeLoc::dump() call.

It would also be nice to be able to invoke `clang` to dump a typeloc
somehow, like `clang -cc1 -ast-dump`. But I don't know exactly what the
best verison of that is, so this patch doesn't do it.

---

There are similar (less critical!) nodes: TemplateArgumentLoc etc,
these also don't have dump() functions today and are obvious extensions.

I suspect that we should add these, and Loc nodes should dump each other
(e.g. the ElaboratedTypeLoc `vector<int>::iterator` should dump
the NestedNameSpecifierLoc `vector<int>::`, which dumps the
TemplateSpecializationTypeLoc `vector<int>::` etc).

Maybe this generalizes further to a "full syntactic dump" mode, where
even Decls and Stmts would print the TypeLocs they lexically contain.
But this may be more complex than useful.

---

While here, ConceptReference JSON dumping must be implemented. It's not
totally clear to me why this implementation wasn't required before but
is now...