extract process_message and remove MessageProcessor struct (#4426) #8814

Job	Run time
ios (macos-13, aarch64-apple-ios)	4m 25s
ios (macos-13, x86_64-apple-ios)	3m 37s
ios (macos-13, aarch64-apple-darwin)	2m 36s
ios (macos-13, x86_64-apple-darwin)	2m 57s
android (ubuntu-20.04, x86_64-linux-android)	2m 19s
android (ubuntu-20.04, aarch64-linux-android)	2m 32s
android (ubuntu-20.04, i686-linux-android)	2m 24s
android (ubuntu-20.04, armv7-linux-androideabi)	2m 39s
error_reporting	0s
	23m 29s

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