Blender Git Loki

UI: Tooltip for data-block selector menus, showing full name and library info

Long data-block names are clipped to fit into data-block selector menus. For
linked data-blocks, there's also a hint indicating the source library, which
takes further space and may get clipped too.

So this commit adds a tooltip to the menu items, which displays the full,
unclipped data-block name and the unclipped library name. Plus, the library
path is shown too, which is also useful info.

Adds helper functions for search menu item tooltips, so these are easier to add
to other search menus in future.

Part of T84188.