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

[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

[alexandar-mitsev]

(partial review)

• the error for popovers without opener is back
  To reproduce - set resizable: true for all popovers at Popover.html test page.
  The console has the exception:
  Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'getBoundingClientRect')
  at PopoverResize.getResizeHandlePlacement (PopoverResize.ts?t=1766136059469:80:31)
  at PopoverResize.setCorrectResizeHandleClass (PopoverResize.ts?t=1766136059469:57:18)

[TeodorTaushanov]

(partial review)

• the error for popovers without opener is back
  To reproduce - set resizable: true for all popovers at Popover.html test page.
  The console has the exception:
  Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'getBoundingClientRect')
  at PopoverResize.getResizeHandlePlacement (PopoverResize.ts?t=1766136059469:80:31)
  at PopoverResize.setCorrectResizeHandleClass (PopoverResize.ts?t=1766136059469:57:18)

Done

[alexandar-mitsev]

this seems to result in wrong placement of resize handle sometimes. The handle moves to the correct spot only after the user clicks on it. Maybe the position should be re-calculated once more after open, but before the user clicks on it

To reproduce - use Popover.html, first sample in section Dynamic. When you click the three dots and open the popover - the handle is bottom right, but if you drag it it moves to bottom left.