cli: refactor FileOutput and Formatter

[bastimeyer]

• add streamlink_cli.utils.path.replace_path
• refactor streamlink_cli.utils.formatter.Formatter
  • rename filename() to path() and return a pathlib.Path object
  • format path parts separately
  • replace dot and double-dot path parts if not explicit user input
  • replace unsupported chars in path parts (like before)
• refactor streamlink_cli.output.FileOutput
  • turn filename into a Path object
  • create parent directories before creating the file descriptor
• update streamlink_cli.main accordingly
• update and add new tests

---

resolves #4081

$ streamlink -o '{author}/{category}/{title}.ts' twitch.tv/dota2ti best
[cli][info] Found matching plugin twitch for URL twitch.tv/dota2ti
[cli][info] Available streams: audio_only, 160p (worst), 360p, 480p, 720p, 720p60, 1080p60 (best)
[cli][info] Opening stream: 1080p60 (hls)
[plugins.twitch][info] Will skip ad segments
[plugins.twitch][info] Low latency streaming (HLS live edge: 2)
[plugins.twitch][info] Waiting for pre-roll ads to finish, be patient
[stream.hls][info] Filtering out segments and pausing stream output                                                                     [stream.hls][info] Resuming stream output
[download][.. - Group Stage Day 4.ts] Written 8.0 MB (9s @ 839.8 KB/s)                                                                          ^C[cli][info] Stream ended
Interrupted! Exiting...
[cli][info] Closing currently open stream...

$ ls dota2ti/Dota\ 2/Dota\ 2\ The\ International\ -\ Group\ Stage\ Day\ 4.ts 
'dota2ti/Dota 2/Dota 2 The International - Group Stage Day 4.ts'