Migrate common processor code to internal #1087

Job	Run time
Unit tests (Go)	1m 4s
Discover supported schema versions	2s
Unit tests (Python)	34s
Static analysis	2m 56s
Build snapshot artifacts	1m 2s
CLI tests (Python)	6m 11s
Acceptance tests (1)	19m 19s
Acceptance tests (2)	20m 30s
Acceptance tests (3)	21m 49s
Acceptance tests (4)	24m 10s
Acceptance tests (5)	23m 19s
CLI tests (Go-Linux)	42s
	2h 1m 38s

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