Add testdox format

[bitfield]

This format shows test names as full sentences, which is useful both for autogenerating documentation ("dox"), and for encouraging programmers to write their test names as sentences describing the behaviour of the unit under test.

The specific method of formatting test names as sentences is that used by https://github.com/bitfield/gotestdox.

[bitfield]

I pushed a commit to use the same icons we use in other formats. There's a --format-hivis option to change the icons to more colorful ones. In a future version we might look at making those the default.

I leave that up to you, of course. But you might be interested to know why gotestdox uses the emojis it does. One of my first users was a blind developer who uses a screen reader, and he reported that the ✘ emoji I was using is pronounced by the screen reader as something like "heavy ballot x", which is weird (gotestsum's is pronounced "heavy multiplication x", which is even weirder). Changing it to simply x made the output a lot more accessible for him.

[dnephin]

Ah, I had not considered screen readers but that's a great point! I'd love to provide some better support. Maybe --format-audible or something like that could change the x to "failed test", etc? The pattern here for switching between the original icons and the new hivis icons seems like it would make it easy to switch to other options as well.

Thank you for explaining the design decisions in gotestdox!

[afbjorklund]

I added --format-icons text, which outputs "PASS" for ✓, "SKIP" for ∅ and "FAIL" for ✖

https://github.com/gotestyourself/gotestsum/pull/366#issuecomment-1699759852