Add IntelliSense explain mode

[jrieken]

Developing IntelliSense is not alway easy, there is many ways how suggestions are sorted and filtered and it would be nice to have some kind of explain mode. E.g. with the details/doc show debug info about

• what was compared against what, e.g con against console and what's the score
• what was the original score (based on lexo-sort, filterText)
• was there a locality bonus?
• maybe timings?
• show items that didn't match

[jrieken]

PR #76294 adds the following

• keybinding Ctrl/Cmd+/ to toggle explain mode (kept till restart or toggled again)
• once enabled it replaces the suggest details widget with
• the provider that added the selected suggestion
• the score that is computed by comparing a prefix against the suggestion
• the distance from a similar word (control by the localitybonus-setting)
• the index derived from the sortText/label

[usernamehw]

I don't think Ctrl+/ is a great keybinding since the action toggle comment will be used much more often (even with suggestVidgetVisible). It looks like this feature is going to be used mostly by extension authors and they can assign the keybinding themselves.