feat: add ability to overlap notes and messages

[twpol]

:bookmark_tabs: Summary

Add ability to overlap (in time) notes and messages in a sequence diagram with new directive par_over

Resolves #2087

:straight_ruler: Design Decisions

• This new directive works the same as par except: each message or note inside is positioned with the same top position
• The code currently only checks for the innermost loop being par_over, since it is not immediately clear what should happen in other cases
• Because the messages and notes are always vertical aligned to the top, messages with a variable number of lines of text aren't lined up

:clipboard: Tasks

Make sure you

• [x] :book: have read the contribution guidelines
• [x] :computer: have added unit/e2e tests (if appropriate)
• [x] :bookmark: targeted develop branch

[jgreywolf]

@twpol Any updates?

[twpol]

@twpol Any updates?

Unfortunately, the 11 months of no engagement has left this with a load of conflicts, and I have long-since moved on

I might be persuaded to resolve the conflicts, but I am unlikely to be willing to make anything more than cosmetic changes for reviews at this point in time

[Yokozuna59]

Since it has been implemented in #4370, I guess we should close this, am I right @jgreywolf?