Support disting in soong-only builds

Disting was normally handled by the packaging kati step, which was
not run in soong-only builds. Disting needs to be done in a separate
ninja file, so that if you toggle dist on/off you only need to
regenerate a small ninja file instead of the main one.

This change makes it so that the kati packaging step is also run in
soong-only builds. (which makes them not technically soong-only, but
the packaging step is very fast so it's fine)

Phonies in soong were normally exported to the main make invocation
and then make would emit the ninja rules for them. In soong-only builds
soong would emit the ninja phone rules directly. This is problematic
when supporting disting in soong, because some of the phony rules have
the same name as dist targets, causing ninja to complain about duplicate
rules. To resolve this, make soong export its phonies to the packaging
step, which will dedup them with the dist phonies.

Bug: 388312357
Test: m --soong-only dist
Change-Id: I1ebf164541173804a2c0c01a5a3b1b139fbf139b