Make TerminalWriter public API?

[The-Compiler]

Looking at the fallout of the py dropping, it seems like one recurrent issue is that people create their own py.io.TerminalWriter:

• pytest-xdist
• pytest-benchmark
• pytest-xprocess

...and probably a lot more!

sooo... I wonder if we should make it public API of some kind, given how it's used like one even in pytest-dev plugins?

[nicoddemus]

Not sure, we probably don't want to encourage users to use that, given we want to eventually drop TerminalWriter in favor of something else (unless I'm wrong in that aspect).

[RonnyPfannschmidt]

Given the capture interaction, its a minefield, nobody should construct them

[asottile]

Config.get_terminal_writer exists -- though afaict it's undocumented