The test was added in #147252. On a 32-bit target, it fails with error:
```
  File "...\TestDataFormatterLibcxxInvalidString.py", line 23, in test
    self.skip()
    ^^^^^^^^^
AttributeError: 'LibcxxInvalidStringDataFormatterTestCase' object has no attribute 'skip'
```

Make the existing libc++ formatter generic
Add initializer_list summary provider.
Add test for `libstdcpp`

PDB doesn't include the typedefs for types, so all types use their full
name. For `std::string` and friends, this means they show up as
`std::basic_string<char, std::char_traits<char>, std::allocator<char>>`.

This PR updates the `std::{,w,u8,u16,u32}string(_view)` tests to account
for this and runs them with PDB.

This enables testing with PDB for all tests that don't require any
changes to pass. I ran the
`lldb/test/API/functionalities/data-formatter/data-formatter-stl/generic`
tests locally and they passed.

Both of these fail on our Clang-19 macOS bots.

From
https://github.com/llvm/llvm-project/pull/163077#issuecomment-3396435083:
Currently, `std::atomic<T>` will always use the MSVC STL synthetic
children and summary. When inspecting types from other STLs, the output
would not show any children.

This PR adds a check that `std::atomic` contains `_Storage` to be
classified as coming from MSVC's STL.

Fixed in https://github.com/llvm/llvm-project/pull/156033

These no longer compile because the warning now defaults to an error
after #157364, so downgrade the error to a warning for now; I’m not
familiar enough with either LLDB or MacOS to fix these warnings properly
(assuming they’re unintended).

The build step is overidden so it uses `libstdc++` instead of `libc++`
on linux

This came up in https://github.com/llvm/llvm-project/issues/155691.

For `std::basic_string` our formatter matching logic required the
allocator template parameter to be a `std::allocator`. There is no
compelling reason (that I know of) why this would be required for us to
apply the existing formatter to the string. We don't check the
`allocator` parameter for other STL containers either. This meant that
`std::string` that used custom allocators wouldn't be formatted. This
patch relaxes the regex for `basic_string`.