fix: SequenceDiagram: draw activations even without explicit deactivation

[dansseg]

:bookmark_tabs: Summary

Activations will now also be drawn, even if there is no deactivation for a participant. The activation will reach down to the bottom or to the point where the participant gets destroyed.

sequenceDiagram
    A ->>+ B : ActivateMe
    B ->> A : NoNeedToDeactivate

Resolves #3849

:straight_ruler: Design Decisions

All activations were already parsed correctly and stored in 'bounds.activations'. If no deactivation was existing, it would remain inside this array. This information is now used to draw the 'missing' activations after all actors and messages were drawn already. If an actor was destroyed, it's last y position is also stored already (bounds.models.actors[].stopy), which will then be used as the end of the activation, instead of the end of the diagram.

:clipboard: Tasks

Make sure you

• [x] :book: have read the contribution guidelines
• [ ] :computer: have added necessary unit/e2e tests.
• [x] :notebook: have added documentation. Make sure MERMAID_RELEASE_VERSION is used for all new features.
• [x] :bookmark: targeted develop branch

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Codecov Report

Attention: Patch coverage is 0% with 17 lines in your changes are missing coverage. Please review.

Project coverage is 5.72%. Comparing base (3809732) to head (2b9d052).

Additional details and impacted files

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