Implement TypeIs (PEP 742) #12078

Job	Run time
Test mypyc suite with 32-bit Python	8m 0s
Test suite with py38-ubuntu, mypyc-compiled	20m 21s
Test suite with py38-windows-64	27m 0s
Test suite with py39-ubuntu	18m 46s
Test suite with py310-ubuntu	18m 22s
Test suite with py311-ubuntu, mypyc-compiled	17m 35s
Test suite with py312-ubuntu, mypyc-compiled	20m 18s
mypyc runtime tests with py39-macos	4m 59s
mypyc runtime tests with py38-debug-build-ubuntu	5m 18s
Type check our own code (py38-ubuntu)	1m 47s
Type check our own code (py38-windows-64)	2m 34s
Formatting and code style with Black + ruff	43s
	2h 25m 43s

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