[mini.pick] Handle case when there is only one element to select

[kascote]

I was reading the help and docs and was unable to find a way to automatically make a selection when there is only one option to pick.
My use case is with require("mini.extra").pickers.lsp for a 'go to definition' hot hey. Most of the time there is only one reference.
TIA

[echasnovski]

Take a look at #978. Specifically this comment for justification (with links to more details) and this comment for inspiration about possible solution.

[kascote]

💯 makes sense. thanks for the code example!