EVP_PKEY_get_size.pod and provider-keymgmt.pod: document their relation #1503

Job	Run time
cygwin (windows-2019, win64, -DCMAKE_C_COMPILER=gcc --strict-warnings no-fips)	36m 44s
minimal (windows-2019)	12m 2s
minimal (windows-2022)	15m 20s
plain (windows-2019)	22m 19s
plain (windows-2022)	23m 55s
shared (windows-2019, win64, enable-fips)	36m 36s
shared (windows-2019, win32, --strict-warnings no-fips)	40m 19s
shared (windows-2022, win64, enable-fips)	49m 12s
shared (windows-2022, win32, --strict-warnings no-fips)	50m 4s
	4h 46m 31s

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