[7.1.x] Migrate build process from npm to yarn

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: 7.1.X
• Fix Version/s: 7.1.X
• Component/s: Frontend Infrastructure
• Labels:
  • 7110-sp-pending
• Branch Version/s:
  7.1.x
• Backported to Branch:
  Committed
• Epic Link: fi-yarn-migration-old-branches
• Sprint: S03E05 - Zagreb, S03E06 - Valencia
• Git Pull Request: https://github.com/liferay/liferay-portal-ee/pull/15338

Our current build process for our frontend code is based on NPM. The NPM CLI has some limitations that make it consume huge amounts of disk and network for a project our size and needs.

For that reason, we've successfully migrated `master`, `master-private`, `7.2.x` and `7.2.x-private` to Yarn as part of LPS-91967

The goal of this task is to apply the necessary build and code changes so we can migrate `7.1.x` build process as well. This is not a straight backport as many different things need to be tweaked, so we're opting for a specific LPS to keep track of things.