This PR uses the new APIs from #21015 to provide a WebUI Add Torrent experience more closely matching the GUI's.
New functionality:
- View torrent size, date, infohash, files, etc.
- Reprioritize and ignore files before adding
- Specify tags when adding torrent
- Specify save path for incomplete torrent
Closes#20557, closes#10997, closes#12499, closes#14201, closes#15071, closes#15718, closes#16207.
PR #21645.
