live-preview: Popup a list of eleemnts at a position when right-clicking on select-mode

[hunger]

This PR adds a new popup that shows when right clicking somewhere in the preview area in select-mode.

It has a list of all the elements at that position with a little bit of extra information and you can select any of them by clicking on them.

[hunger]

I am not yet completely happy with this PR, but it is starting to come together.

The popup size and popup location can still use improvement and the scrolling is erratic at times...

I also need to shorten the file names this thing shows :-)

But as a side-effect: This PR has caused some selection bugs to be fixed already and includes a bit of fine-tuning of the selection.

[hunger]

We really need to improve the popup more:-/

[tronical]

I also need to shorten the file names this thing shows :-)

Suggestion: strip the common prefix for all paths. And in the future, preserve library mappings (and exclude from stripping).

[hunger]

@simon: "Zwei Dumme ein Gedanke" :-)

[szecket]

has turned into

it appears the name := assigned to the component was lost

also, the top item here is supposed to be in the controls_page.slint but isn't

[hunger]

@szecket: I was wondering how long you would take to spot this:-)

I need the frames to all have the same height all the calculations are off.

[szecket]

can you be more specific about "the frames"? the preview or the container for all the info for each selectable item?

[hunger]

@szecket: The element I add into the list view that gets added in the for loop. The file name was (conditionally) above the Rectangle which all preview and the text fields with extra information.

[szecket]

with our changes, this looks quite good!