Improvements to database migrations

[ajcvickers]

This is a grouping of related issues. Feel free to vote (👍) for this issue to indicate that this is an area that you think we should spend time on, but consider also voting for individual issues for things you consider especially important.

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This an "epic" issue for the theme of miscellaneous improvements to Migrations. Specific pieces of work will be tracked by linked issues.

Done in 6.0

• [x] #10059
• [x] #21252

Done in 7.0

• [x] #10695
• [x] #11162
• [x] #21765

Backlog

• [ ] #14545
• [ ] #18950
• [ ] #15854
• [ ] #13146
• [ ] #28226
• [ ] #6546
• [ ] #10258
• [ ] #14075
• [ ] #11548
• [ ] #15178
• [ ] #18708
• [ ] #19710
• [ ] #20159
• [ ] #27729
• [ ] #20391
• [ ] #20592
• [ ] #20692
• [ ] #20723
• [ ] #20931
• [ ] #21779
• [ ] #21964
• [ ] #10660
• [ ] #22515
• [ ] #1775
• [ ] #16758
• [ ] #16964
• [ ] #2100
• [ ] #26115
• [ ] #12586
• [ ] #18965
• [ ] #22598
• [ ] #20475