pkcs5: simple `pbes2::Params` constructors #1490

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	2m 19s
build (1.65.0, wasm32-unknown-unknown)	2m 50s
fuzz	2m 30s
build (stable, thumbv7em-none-eabi)	57s
build (stable, wasm32-unknown-unknown)	50s
test (1.65.0)	21m 47s
test (stable)	17m 17s
minimal-versions / minimal-versions	13m 14s
	1h 1m 44s

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