Add site-packages watchers #2796

Job	Run time
Create VSIX	32s
Lint	20s
TypeScript Unit Tests (ubuntu-latest)	20s
TypeScript Unit Tests (windows-latest)	1m 6s
Integration Tests	0s
Smoke Tests	-1s
Integration Tests (Multi-Root)	0s
E2E Tests	0s
	2m 17s

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