build: switch to yarn

[devversion]

Switches away from package-lock.json to yarn.lock because the NPM lock files are not platform independent and change based on optionalDependencies that can be installed.

Since the lock file always changes after NPM install on CircleCI, the cache key will be always different, and therefore never available for the next commit that runs on the CI.

Note: This is based on top of #13359 and should be merged once #13359 has been merged.

[devversion]

This should be ready now. The e2e failure is unrelated and should be fixed with #13376

[jelbourn]

LGTM

In preparation for merging this, we need to make sure everyone has yarn set up

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "continuous-integration/travis-ci/pr" is failing

If you want your PR to be merged, it has to pass all the CI checks.

If you can't get the PR to a green state due to flakes or broken master, please try rebasing to master and/or restarting the CI job. If that fails and you believe that the issue is not due to your change, please contact the caretaker and ask for help.

[jelbourn]

@devversion could you rebase?

[devversion]

@jelbourn Should be good now. Let's wait for CircleCI to finish.

[ngbot]

Hi @devversion! This PR has merge conflicts due to recent upstream merges.
Please help to unblock it by resolving these conflicts. Thanks!

[devversion]

This one is good to go now.

[angular-automatic-lock-bot]

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