feature/plural: move and regenerate remaining code

Move parts of code and do some renaming.

Manually change go generate directives and added new package to
x/text/gen.go

Regenerate tables for original and destination package.

Change-Id: I728dde1c0f7dcc289372fb815ecc4ed85d182cc2
Reviewed-on: https://go-review.googlesource.com/39132
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>