Update issuable lists: part 2

What does this MR do and why?

Note: this is part 2 of many to get to something sort of like the design in Issue list row re-design (#22482 - closed)

Updates design of issuable lists:

• Make icons smaller
• Use gray-500 for all sub text
• Use smaller font for MR task list to match issues
• Move issue type icon to title row

What does this MR not do?

• Anything to the epics list

Part 1: Update issuable lists: part 1 (!118062 - merged)

Screenshots or screen recordings

	Before	After
Merge requests
Issues

How to set up and validate locally

Look at MR and issues lists

#398228 (closed)