Improve devtools visual elements

[GuiltyDolphin]

Reviewer: @jonathanKingston

CC: @kzar

Description:

https://app.asana.com/0/312629933896096/1202714468322458/f

This adds some visual improvements to the devtools panel, to make working with it easier:

• on/off visibility
  • disabled protection buttons now highlight in red, enabled in green
• current selection visibility
  • when hovering over a table cell, the cell and row will be highlighted for extra visibility
  • the contents of the hovered cell will expand if necessary (i.e., if the contents are cut short) to make the full contents visible
  • hovering over protection buttons will also change their colour slightly to indicate the hover
• fixes colouring on set-cookie-tracker rows (were not highlighting before)
• updates the red colour for "blocked" to be less harsh, easier on the eyes
• adds follow scrolling for the protections panel and table header
  • previously, you would have to scroll all the way to the top of the document to access the protection buttons, but now they will be accessible wherever you scroll

Steps to test this PR:

1. Navigate to a web page
2. Open dev panel and set the target to the webpage. Reload the page
3. Check scrolling
   1. Scroll - the button panel should follow the scrolling
   2. Resize the window to be smaller, scoll
   3. The table header should remain at the bottom of the protections panel, and should scroll with you
4. Check that set-cookie-tracker rows have a blue/purple colouring
5. Check that hovering over cells highlights them and shows a border around the row
6. Check that blocked rows have a pale red colouring
7. Check feature buttons
   1. Check that enabled features are in green, disabled in red
   2. Toggle a feature, click "Reload page" at the top of the panel
   3. The feature colour should match the new protection status
8. Check cell content display
   1. Resize window to be small until cells show "..." at the end
   2. Hover over these cells
   3. Full cell contents should be visible
   4. Move cursor away, cell should should the "..." again

Automated tests:

• Unit tests
• Integration tests

Reviewer Checklist:

• Ensure the PR solves the problem
• Review every line of code
• Ensure the PR does no harm by testing the changes thoroughly
• Get help if you're uncomfortable with any of the above!
• Determine if there are any quick wins that improve the implementation

PR Author Checklist:

• Get advice or leverage existing code
• Agree on technical approach with reviewer (if the changes are nuanced)
• Ensure that there is a testing strategy (and documented non-automated tests)
• Ensure there is a documented monitoring strategy (if necessary)
• Consider systems implications