Further improvements to functools.partial handling #12771

Job	Run time
Test mypyc suite with 32-bit Python	7m 3s
Test suite with py38-ubuntu, mypyc-compiled	17m 32s
Test suite with py38-windows-64	19m 39s
Test suite with py39-ubuntu	16m 14s
Test suite with py310-ubuntu	15m 38s
Test suite with py311-ubuntu, mypyc-compiled	15m 30s
Test suite with py312-ubuntu, mypyc-compiled	18m 1s
mypyc runtime tests with py39-macos	4m 36s
mypyc runtime tests with py38-debug-build-ubuntu	4m 22s
Type check our own code (py38-ubuntu)	1m 56s
Type check our own code (py38-windows-64)	2m 28s
Formatting and code style with Black + ruff	33s
	2h 3m 32s

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