feat(ui5-popover): implement resizable popover

[TeodorTaushanov]

JIRA: BGSOFUIRODOPI-3384

Certain styles for slotted elements in the footer and header are overridden, similar to how it is done in the UI5 dialog.

fixes #8167
fixes #12088

[ui5-webcomponents-bot]

🚀 Deployed on https://pr-12623--ui5-webcomponents-preview.netlify.app

[alexandar-mitsev]

• during the resize, the arrow constantly flickers. minor issue, but quite visible.
• sometimes the resize arrow is on the wrong side. This happens if the opener is longer than the popover - e.g. in a very long date picker input, the popover is in leftmost position and the arrow is also in the left bottom arrow. To reproduce set resizable to true on the datepicker input (second input) on test/pages/Popover.html. Same is reproducible in the "Horizontal Align" test section in Popover.html
• during resize - if you do it quick, the resizing starts to lag. Can stay like that, but if possible to fix, will be better

[TeodorTaushanov]

• during the resize, the arrow constantly flickers. minor issue, but quite visible.

• this can be changed with another change. It is going to be a difficult fix.

• sometimes the resize arrow is on the wrong side. This happens if the opener is longer than the popover - e.g. in a very long date picker input, the popover is in leftmost position and the arrow is also in the left bottom arrow. To reproduce set resizable to true on the datepicker input (second input) on test/pages/Popover.html. Same is reproducible in the "Horizontal Align" test section in Popover.html

• Fixed.

• during resize - if you do it quick, the resizing starts to lag. Can stay like that, but if possible to fix, will be better

• I'm not able to reproduce it.

[TeodorTaushanov]

• during the resize, the arrow constantly flickers. minor issue, but quite visible.

• It is improved a bit.

[Stoev]

Looks good from my UA perspective.

[alexandar-mitsev]

1. now a popover opened from the right edge of the screen has the resize handle also on the right edge. See screenshot

2. with the latest changes, if you make this sample "Test open popup and hide opener
   " resizable, it can not be resized - the popover hides the moment you click on the resize handle

[alexandar-mitsev]

you may consider moving all those private properties and most of the resize related logic inside a second class, e.g. PopoverResize.ts. It can contain the methods you need, like getResizeHandleClasses, onClose, attachMouseEvents, reset, isResizeHandleClicked and etc.
This will make the Popover.ts easier to read.
Could be separate BLI