Activate linting to legacy JS

• Type: Task
• Status: Closed
• Priority: Minor
• Resolution: Completed
• Affects Version/s: None
• Fix Version/s: 7.2.10 DXP FP2, 7.2.10.1 DXP SP1, 7.2.X, Master
• Component/s: Frontend Infrastructure
• Labels:
  • liferay-dxp-72-sp1
  • liferay-fixpack-dxp-2-7210
• Branch Version/s:
  7.2.x
• Backported to Branch:
  Committed
• Epic Link: fi-frontend-guidelines
• Sprint: S03E08- Seoul
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/77990

In our current state, we have 2 sets of files:

• current: *.es.js
• legacy: .js && !.es.js

We have 2 main ways to enforce consistency and correctness in our JS code:

• Fomatting with Prettier. This is applied to both current and legacy code
• Linting via ESLint. This is applied only to current code

The goal of this task is to apply linting also to legacy code to provide a safer environment to our developers needing to modify that code in the future and to simplify the overhead of switching contexts.