Check in initial diff engine and semantic analysis #6

Job	Run time
Security Audit	5m 7s
Test Suite (ubuntu-latest, stable)	22s
Test Suite (windows-latest, stable)	31s
Test Suite (macos-latest, beta)	35s
Test Suite (macos-latest, stable)	22s
Test Suite (windows-latest, beta)	33s
Test Suite (ubuntu-latest, beta)	37s
Build Release	0s
	8m 7s

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