Check in initial diff engine and semantic analysis #3

Job	Run time
Security Audit	5m 2s
Test Suite (ubuntu-latest, beta)	32s
Test Suite (ubuntu-latest, stable)	27s
Test Suite (windows-latest, stable)	27s
Test Suite (windows-latest, beta)	34s
Test Suite (macos-latest, beta)	29s
Test Suite (macos-latest, stable)	22s
Build Release	0s
	7m 53s

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