hide ElementBoxWidget label to meet size constraint

[Ichthyostega]

As lumiera developer,
I want ElementBoxWidget to automatically manage and hide the ID label,
to allow for adhering to external size constrains due to calibrated timeline display

Acceptance Criteria

Given

• running Lumiera UI
• instance of ElementBoxWidget with non-empty Name-ID

When

• a horizontal size constraint is imposed on construction of the widget
• And the rendered Text label widget with the given Name-ID would violate that constraint

Then

the nested label widget will be hidden and removed from display

[Ichthyostega]

The way how to deal with size-constrained widgets seems basically clear by now, indicating also how to solve the first part of this problem here: not showing the label right from start -- unless there is enough space to render it. What remains to be done is to also hide the label on changing size constraints (which will happen when chaning the zoom scale on the timeline display)

[Ichthyostega <prg@…>]

In ea53ef34/Lumiera:

ElementBox: coping with size constraints (closes #1238)

devise a more fine grained algorithm for adapting the display of IDLabel
to a situation with size constrained layout, e.g. for a time calibrated canvas.
We still do not implement the shortening of ID labels (see #1242),
since doing so would be surprisingly expensive. But at least we
do proceed in several steps now

• first attempt to reduce the name-ID (for now: hide it)
• if this doesn't suffice, also hide the menu
• and as a last resort, hide the icon and thus make the IDLabel empty

[Undercover Agent]

Migration MasterTickets ⟼ Subtickets-plugin