Refactoring of RichStream.from(Optional)
Refactoring of RichStream.from(Optional)

Summary: As suggested in D15194495, split into separate diffs.

Reviewed By: styurin

fbshipit-source-id: f77d78b396

Addepar/buck,JoelMarcey/buck,facebook/buck,nguyentruongtho/buck,Addepar/buck,nguyentruongtho/buck,zpao/buck,Addepar/buck,nguyentruongtho/buck,zpao/buck,nguyentruongtho/buck,kageiit/buck,JoelMarcey/buck,JoelMarcey/buck,facebook/buck,zpao/buck,Addepar/buck,JoelMarcey/buck,zpao/buck,kageiit/buck,JoelMarcey/buck,facebook/buck,kageiit/buck,JoelMarcey/buck,Addepar/buck,Addepar/buck,Addepar/buck,kageiit/buck,Addepar/buck,nguyentruongtho/buck,facebook/buck,zpao/buck,nguyentruongtho/buck,JoelMarcey/buck,JoelMarcey/buck,facebook/buck,nguyentruongtho/buck,Addepar/buck,JoelMarcey/buck,JoelMarcey/buck,Addepar/buck,facebook/buck,kageiit/buck,JoelMarcey/buck,kageiit/buck,Addepar/buck,facebook/buck,Addepar/buck,Addepar/buck,zpao/buck,kageiit/buck,JoelMarcey/buck,zpao/buck,JoelMarcey/buck