Add button to start thread on reply

[filipesmedeiros]

Description

The only thing the above PR does is add a button to the message popup if it is not yet inside a thread to start a thread. It looks like this:

The button only shows up if the message hovered is not inside a thread itself. It works nicely. The way threads in Matrix works makes it so that if you reply to a message that is already a thread root, it doesn't matter. The new threaded reply will just be added to the end of the thread. Nice!

Fixes #2308

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[github-actions[bot]]

All contributors have signed the CLA ✍️ ✅
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[filipesmedeiros]

I have read the CLA Document and I hereby sign the CLA

[github-actions[bot]]

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[filipesmedeiros]

@ajbura added a screenshot of the new icon to the original post :)

[GimleLarpes]

Should the new thread button also be added to the context menu? To me it would make sense that the hover/quickaccess-popup is a subset of the buttons in the full pop-up menu, and so it feels a bit weird that something is only in the quick-access popup.

[filipesmedeiros]

Added @GimleLarpes :) Thanks for the great suggestion!

[GimleLarpes]

~~Pedantic note, but the T in "Reply in Thread" should be capitalized 😅~~ nvm I can't read lol