Add text encoder conversion (#1559)
* Initial code for attempt at improving SD <--> diffusers conversions for v2.0
* Updates to support round-trip between orig. SD 2.0 and diffusers models
* Corrected formatting to Black standard
* Correcting import formatting
* Fixed imports (properly this time)
* add some corrections
* remove inference files
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
