Allow inferring +int to be a Literal #12049

Job	Run time
Test suite with py38-ubuntu, mypyc-compiled	19m 12s
Test suite with py38-windows-64	27m 38s
Test suite with py39-ubuntu	18m 32s
Test mypyc suite with 32-bit Python	8m 5s
Test suite with py310-ubuntu	18m 6s
Test suite with py311-ubuntu, mypyc-compiled	17m 28s
Test suite with py312-ubuntu, mypyc-compiled	19m 48s
mypyc runtime tests with py39-macos	9m 54s
mypyc runtime tests with py38-debug-build-ubuntu	5m 22s
Type check our own code (py38-ubuntu)	1m 54s
Type check our own code (py38-windows-64)	2m 22s
Formatting and code style with Black + ruff	45s
	2h 29m 6s

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