Draft: Introduce --print-selected-count

[resolritter]

Disclaimer: I know this is missing tests, documentation, indentation, etc... which is why I'm opening this as a Draft first. I'd like to know if you are willing to accept this solution before going further with the rest.

Problem

Since FZF falls back to the current item even if nothing is selected, there's no way to differentiate between the two situations:

• In multi-mode, one item was selected and FZF exited with it
• No item was selected, but the item under the cursor was chosen as a fallback

fzf/src/terminal.go

Lines 577 to 578 in 0db65c2

	if !found {
	current := t.currentItem()

Solution

This MR would introduce a print-selected-count option, which is useful to disambiguate, in multi selection mode, if an "expected" binding has exited with an explicit multi-selection instead of the aforementioned fallback behavior.

At the same time, this would also be useful for some other use-case which would like to have the result count without extra post-processing.