Rework get_raw_message to return `StreamMessage` #4399

Job	Run time
check examples (ubuntu-latest / stable)	56s
check docs (ubuntu-latest / stable)	1m 18s
check feature flags (ubuntu-latest / stable)	9m 39s
check format (ubuntu-latest / nightly)	13s
check licenses (ubuntu-latest / stable)	22s
check linter (ubuntu-latest / stable)	1m 29s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	41s
check minimal supported rust version (ubuntu-latest / msrv)	27s
check spelling (ubuntu-latest / nightly)	27s
test (ubuntu-latest / stable)	7m 39s
test (macos-latest / stable)	8m 27s
test (windows-latest / stable)	11m 54s
	43m 32s

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