PR that refacto content.js code and handle a new job section with tag filtering & options to hide annoying sections

• Refactor content.js
  - Code splitting for content.js in multiple modules: feed, general, jobs, misc & message. Utils & constants files are used to share code
  - Improved unhiding handling in every features
  - Made hideByClassName more aggressive to tackle LinkedIn "ads protection" that prevents us from hiding some ads & premium prompts

• Job section
  - Filter jobs by keyword
  - Hide AI button
  - Hide Job Guidance section
  - Hide Promoted Jobs

• Broken features fixed
  - select message for deletion
  - ads hiding
  - videos hiding
  - premium hiding
  - unhiding on specific options
  - unfollow all option
  - Hide post by age

For code splitting:

• content.js dynamically import features/index.js so it can use ES6 imports
• In index.js, we setup event handler to start the logic
• In features/*.js files, we export functions associated with each tab (general, misc, job & feed) or features like messages
• In utils, we put all shared functions
• In constants, we put all shared constants