Add basic support for recursive TypeVar defaults (PEP 696) #12056

Job	Run time
Test mypyc suite with 32-bit Python	8m 10s
Test suite with py38-ubuntu, mypyc-compiled	18m 30s
Test suite with py38-windows-64	26m 23s
Test suite with py39-ubuntu	18m 38s
Test suite with py310-ubuntu	17m 58s
Test suite with py311-ubuntu, mypyc-compiled	17m 14s
Test suite with py312-ubuntu, mypyc-compiled	19m 31s
mypyc runtime tests with py39-macos	5m 1s
mypyc runtime tests with py38-debug-build-ubuntu	5m 29s
Type check our own code (py38-ubuntu)	1m 47s
Type check our own code (py38-windows-64)	2m 23s
Formatting and code style with Black + ruff	39s
	2h 21m 43s

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