This commit adapts the ABI tag as follows:

- It removes ``PYBIND11_INTERNALS_KIND`` that was neither used nor documented.
- It adapts the MSVC ABI tag to be less stringent (see PR pybind#4953)
- It adapts the GCC ABI tag to be less stringent.
- It adds a check for a Clang/libc++ ABI tag that wasn't present before

I plan to make a consistent set of changes to nanobind so that both
libraries use interchangeable platform ABI tags.