Add support for adding icons and tooltips to Tree title columns

[jinsediaoying]

Describe the project you are working on

Custom Editor UI

Describe the problem or limitation you are having in your project

In case of a single checkbox wide column, an icon is better than a text title.
And also tooltips for that icon.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Allow draw a icon to the Tree's title, and add tooltip to it.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

(image from my unity project)

add methods to Tree:
SetColumnIcon (columnIndex, icon);
SetColumnTooltip (columnIndex, tooltip);

If this enhancement will not be used often, can it be worked around with a few lines of script?

icon: use a emoji font may work
tooltip: no idea

Is there a reason why this should be core and not an add-on in the asset library?

maintain a emoji font for this purpose is too complicated

[theraot]

Sometimes posting alternatives or workarounds is useful, in particular if the issue or proposal comes from a time critical project. This is not to encourage a workaround culture, but... Since you seem to be in a hurry, here goes mine: can you do this with an emoji font?

Addendum 1: Ok, that won't work for the tooltip.

Addendum 2: Looking at the source code, it is using custom drawing. I think we could modify get_tooltip to check if the mouse is hovering on the title, the same way the code checks if the tile is being hovered to draw it (https://github.com/godotengine/godot/blob/6afd320984cf14198368cc6c53752813a02169e3/scene/gui/tree.cpp#L4202).