[SemaCXX] Handle lack of TypeSourceInfo on special member functions in templated...

[SemaCXX] Handle lack of TypeSourceInfo on special member functions in templated lambdas

During template instantiation involving templated lambdas, clang
could hit an assertion in `TemplateDeclInstantiator::SubstFunctionType`
since the functions are not associated with any `TypeSourceInfo`:

`assert(OldTInfo && "substituting function without type source info");`

This path is triggered when using templated lambdas like the one added as
a test to this patch. To fix this:

- Create `TypeSourceInfo`s for special members and make sure the template
instantiator can get through all patterns.
- Introduce a `SpecialMemberTypeInfoRebuilder` tree transform to rewrite
such member function arguments. Without this, we get errors like:

`error: only special member functions and comparison operators may be defaulted`

since `getDefaultedFunctionKind` can't properly recognize these functions
as special members as part of `SetDeclDefaulted`.

Fixes PR45828 and PR44848

Differential Revision: https://reviews.llvm.org/D88327