refactor(rust): Add `FromIterator` impls for `PlSmallStr` #11036

Job	Run time
check-wasm	5m 53s
check-features	8m 30s
test (ubuntu-latest)	3m 40s
integration-test (ubuntu-latest)	1m 49s
integration-test (windows-latest)	6m 16s
test (windows-latest)	10m 14s
	36m 22s

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