Add env var to skip TSC

[scinos]

Changes proposed in this Pull Request

Adds env var to skip tsc compilation. Since #47502 we don't need to run tsc to compile the project, we only run it to provide better TypeScript typings for IDEs.

This should shave off ~40s every time we run yarn install in CI (pretty much in every build).

Update: running tsc on yarn postinstall was doing implicit typechecking, failing the build if the are TS type errors. In order to not lose this capability, I added an explicit typecheck when running unit tests.

Testing instructions

• Smoke test live branch to ensure Calypso still compiles
• Verify tests are green
• Check if TeamCity builds are faster compared with trunk (note that Run unit tests will be about the same)

[matticbot]

Test live: https://calypso.live/?branch=build/skip-tsc

[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[simison]

Does the CI run still fail if there are TypeScript errors in branch in some packages that are 100% typed?

[scinos]

Does the CI run still fail if there are TypeScript errors in branch in some packages that are 100% typed?

Good catch @simison ! I've changed the Run type checks step to check all projects in ./packages (like yarn install did before this PR).

[simison]

Added Luna team as reviewer just for visibility since many 100% typed packages are from them, but feel free not to wait for any reviews. :-)

[griffbrad]

🚀 This is working great for me!

[ciampo]

Does the CI run still fail if there are TypeScript errors in branch in some packages that are 100% typed?

That's my question as well — are we still going to be build errors in case of TypeScript errors?

[scinos]

are we still going to be build errors in case of TypeScript errors?

Yes, ts errors in ./packages are validated as part of the Run type checks step in the mandatory Run unit tests build.