Rework get_raw_message to return `StreamMessage` #4375

Job	Run time
check docs (ubuntu-latest / stable)	57s
check format (ubuntu-latest / nightly)	14s
check licenses (ubuntu-latest / stable)	23s
check linter (ubuntu-latest / stable)	1m 21s
check feature flags (ubuntu-latest / stable)	8m 54s
test (ubuntu-latest / stable)	7m 29s
check examples (ubuntu-latest / stable)	46s
test (macos-latest / stable)	2m 53s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	29s
test (windows-latest / stable)	12m 59s
check minimal supported rust version (ubuntu-latest / msrv)	31s
check spelling (ubuntu-latest / nightly)	27s
	37m 23s

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