Feature request: Use Splice as difftool

[sergeda]

It would be great to have ability to use this tool as difftool. Now it requires 4 input buffers and throwing error if they are not provided

[errael]

Greetings @sergeda,

I've just released Splice9; it's pure vim9script, no python; it's compatible with the original Splice with additional features, particularly UI. I've addressed some issues against the original Splice (see below) and I'm curious about this issue's idea of use Splice as a diff tool.

vim has a diff mode; why is that not sufficient? What features/capabilities of splice would you like in a diff tool?

Feature: #30, #15, errael/splice9#16