Check in initial diff engine and semantic analysis #4

Job	Run time
Security Audit	4m 59s
Test Suite (ubuntu-latest, beta)	29s
Test Suite (macos-latest, stable)	23s
Test Suite (ubuntu-latest, stable)	24s
Test Suite (windows-latest, beta)	27s
Test Suite (windows-latest, stable)	28s
Test Suite (macos-latest, beta)	33s
Build Release	0s
	7m 43s

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