Allow tooltips/hovering on symbols in outline view and breadcrumbs

[piersdeseilligny]

Currently, the information which breadcrumbs and the outline view can provide is limited to two strings: the title and the "detail" (breadcrumbs are not even able to display the detail string). For the underlying complexity of the information being presented, this seems quite limiting.

In order to optionally provide more information about a symbol (and without cluttering the UI), it would be really nice if if symbols could at least provide a tooltip, through an extremely simple DocumentSymbol.tooltip: string property (basically identical to the underlying tooltip property of TreeItem).

If this feature were to be taken all the way, hovering over symbols in the breadcrumbs or outline view could display information about the symbol from the document's registered HoverProvider for the symbol's selectionRange. This could be enabled/disabled on a symbol-by-symbol basis (something along the lines of DocumentSymbol.triggerhoverprovider: boolean). This would make the breadcrumbs and outline view significantly more useful for understanding the structure of a document without fully diving into the code.

Bad behaviour

unhelpful, repetitive, ugly: i already know the name of the symbol, it's just there

Good behaviour

helpful, useful, and pretty: the only way I could know what this part of the document does is by clicking the symbol and hovering over it in the editor

DocumentSymbols help explain the structure of the code - why limit this explanation to the name, especially when there's more information about them so readily available?

[fowl2]

note that if the "title" is long, the tooltip displaying it 'again' might not be redundant