chore: minor graphic adjustments to quick actions modal

[madbob]

Here a totally unrequested adjustment of the design of Quick Action edit modal.

Changes are purely aesthetic, no functionality has been changed.

Notable changes:

• margins and spacing
• the d'n'd handle for unsortable actions (Move Thread and Delete Thread) is grayed out, to indicate to the user that those cannot be moved (I tried to drag one of those actions, it didn't worked, I believed I broke something, only reading at the code I found that those cannot be moved and it is normal...)

Working on this I found the bug #13308 which is NOT here targeted.

Those adjustments are subjective and have not been approved by a real designer! Feel free to reject this!

[ChristophWurst]

have not been approved by a real designer

summoning the real @nimishavijay

[hamza221]

Looks good, thank you.

[ChristophWurst]

@madbob small nitpick: please amend and change the commit message to something like fix(ui): improve quick actions modal design

background: I want to backport this, and a chore is for changes that do not change the product. They are not added to the automatic changelog. A fix is always added, and I think this is definitely note-worthy.

[ChristophWurst]

/backport to stable5.10

[madbob]

Fixed commit comment.

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