Experimental support for @semanticNonNull #6939

Job	Run time
JS Tests (Node 14.x)	1m 25s
VSCode Extension Lint	18s
JS Lint	55s
JS Tests (Node 16.x)	1m 30s
Rust Tests (ubuntu-latest)	4m 46s
Compiler output check (ubuntu-latest)	3m 59s
Flow Typecheck	36s
Compiler output check (macos-latest)	5m 51s
Rust Tests (macos-latest)	4m 31s
Rust Tests (windows-latest)	6m 58s
Build Rust Compiler (ubuntu-latest)	3m 38s
Build Rust Compiler (ubuntu-latest)	4m 55s
Rust Lint	17s
Build Rust Compiler (macos-latest)	5m 0s
Build Rust Compiler (macos-latest)	11m 26s
Build Rust Compiler (windows-latest)	6m 22s
Publish to NPM	0s
	1h 2m 27s

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