fix(NcAppSidebar): manage focus only after transition has finished

[ShGKme]

☑️ Resolves

• Fix Switching to a chat from the root page has a UI glitch if sidebar was open before nextcloud/spreed#12747

When NcAppSidebar appears, two things happen:

1. Transition animation with margin
2. Focus is moved to the sidebar

Moving focus scrolls container (NcContent) to the sidebar which is out of the container (in the process of moving from the right side). It results in weird animation when the margin changes the width + scroll of the container instead of the position of the sidebar.

P.S. overflow: hidden only hides the scrollbar and content, but the container is still scrollable.
overflow: clip is used to actually remove scrolling.

Slowed animation 1000 times to see the effect: sidebar moves left and right by 1 pixel.

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• Move focus management to transition hooks
  • Both return focus and focus trap

Alternative solution

Use overflow: clip on NcContent to remove scrolling.

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[Antreesy]

Tested

[ShGKme]

/backport to next