Drop support for yarn@1, set packageManager field in package.json (pn… #918

Job	Run time
Slow tests: defaults with npm	2m 8s
Tests (addon-location)	52s
Tests: Type Check	11s
Slow tests: defaults with pnpm	1m 12s
Tests (test-app-location)	59s
Slow tests: typescript with npm	2m 50s
Tests (addon-only)	28s
Slow tests: typescript with pnpm	1m 37s
Tests (monorepo with npm)	2m 22s
Lint JS	18s
Tests (monorepo with pnpm)	1m 1s
Tests (rollup-build)	1m 6s
Tests (declarations-configuration)	43s
	15m 47s

Provide feedback