fix I/O operation on closed file error with CliRunner and echo_via_pager

[ChrisPappalardo]

Fixes #3449 by adding a thinner version of MaybeStripAnsi that is not subclassed from io.TextIOWrapper when handling sys.stdout and sys.stderr streams.

[davidism]

Seems like we should be able to keep the single wrapper and override the close method to do nothing in the problematic case.

[davidism]

@Rowlando13 this is a good example of why I think the whole text/binary stream handling in Click is not needed. It's completely bypassed for stdin/stdout here, and all tests still pass. Fairly sure these checks were for Python 2/3 compat, but I didn't have enough time to check it all when I removed most of the compat years ago.

[kdeldycke]

This is being discussed at #3481

[davidism]

After investigating from my initial comment, it does look like we need to wrap the stream returned by nullpager instead of this. The wrapper should pass everything through, except override close to do nothing. Will work on this tonight or tomorrow.

[davidism]

Also needed to make sure stream.buffer wouldn't close either, since get_pager_file would wrap stream.buffer instead of stream. This all seems a bit messy, probably something that can be cleaned up eventually. @Rowlando13 @kdeldycke.

[kdeldycke]

Also needed to make sure stream.buffer wouldn't close either, since get_pager_file would wrap stream.buffer instead of stream. This all seems a bit messy, probably something that can be cleaned up eventually. @Rowlando13 @kdeldycke.

Also CC @AndreasBackx for the missing tests in #3405 covering #1572