Rework get_raw_message to return `StreamMessage` #4369

Job	Run time
check docs (ubuntu-latest / stable)	1m 3s
check linter (ubuntu-latest / stable)	1m 21s
check examples (ubuntu-latest / stable)	58s
check feature flags (ubuntu-latest / stable)	8m 18s
check format (ubuntu-latest / nightly)	12s
check licenses (ubuntu-latest / stable)	22s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	37s
check minimal supported rust version (ubuntu-latest / msrv)	37s
check spelling (ubuntu-latest / nightly)	5m 54s
test (ubuntu-latest / stable)	8m 10s
test (macos-latest / stable)	8m 59s
test (windows-latest / stable)	12m 26s
	48m 57s

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