Resolve "Milestone pages have problems on mobile"

What does this MR do?

Makes the milestone page more mobile friendly

Are there points in the code the reviewer needs to double check?

Shouldn't be but maybe double check that the views I changed are exclusively used by the milestone details page I was amending and not any other pages that I haven't tested after my changes.

Why was this MR needed?

• Buttons were misaligned
• Progress bar was not 100% width
• Stats were cut in the middle
• Milestone name/date text overflow

Screenshots (if relevant)

With this MR:

Closes #18852 (closed)