core workflow: simplify file search results display

Created by: novoselrok

Fixes #38566 (closed) Fixes #38182 (closed)

Changes (all contained behind the core workflow temporary setting):

• Add a button for expanding/collapsing matches below the file search result
• Reduce the number of line groups shown by default
• Hide the result type icons

Demo

https://user-images.githubusercontent.com/6417322/179165868-b54bac84-7fb9-45e8-ba76-c180d1e34fda.mov

Test plan

• Disable the core workflow improvements (Simple UI toggle in user settings dropdown)
  • Search results should work the same as before
• Enable Simple UI
  • Run a search
  • You should be able to expand files with a lot of matches
  • No result type icons should appear next to the repo name/file name

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.