PEP 747: Annotating Type Forms

[davidfstr]

Please provide a recommendation on PEP 747 which has been discussed most recently in: https://discuss.python.org/t/pep-747-typeexpr-type-hint-for-a-type-expression/55984

There is a reference implementation in pyright and very nearly a reference implementation in mypy, once I've integrated Jukka's final feedback from PyCon US. No substantive issues have been discovered during the implementation process.