Add the possibility to change mail list view into full width

[GretaD]

Fix #8811

• Requires feat(NcAppContent): add no-split layout + feat(NcListItem): add one-line layout nextcloud-libraries/nextcloud-vue#5209
• Requires fix(NcListItem): change padding for one-line layout nextcloud-libraries/nextcloud-vue#5391

[ChristophWurst]

Noticed during testing

• Back button always causes the envelope list to reload. This seems unnecessary and makes interactions slow.
• Sidebar toggle and back button have inconsistent color (black vs gray) and do not align horizontally.
• Important icon is broken in list mode
• The clickable area and hover area of envelopes is small in list mode. Increase padding and reduce margin at the same rate to make the elements bigger without taking more space.

Other

• Subject/preview is not styled as columns. The longer the subject, the less I see of the preview. This is by design spec but it looks strange.

[st3iny]

• 1. There are two scroll bars when using list layout.
• 2. Scrolling to load more doesn't work on portrait screens
  • This is a know and wont-fix bug of the old layout as well. We just hide it by loading enough messages so that the list is always scrollable. Now, the list fits more items so we should increase the amount of initial envelopes a bit in list mode.

About 1.)

[hamza221]

Current state not indicate, Maybe it should be like this? Horizontal is also possible

B	A

[ChristophWurst]

Has #9285 (review) been addressed?

[ChristophWurst]

Tested and works

Looks great. Works on desktop and mobile 👍

[ChristophWurst]

No more double scrolling bar 👍

whitespace on top of thread header can be improved

[ChristophWurst]

[GretaD]

whitespace on top of thread header can be improved

i will do this in a follow up pr, after the horizontal layout is in as well, because for sure it will need some changes there too