This fixes a signing regression caused be #25751. That changed us to
directly call the SWIX build props / targets vs. getting them implicitly
from the microbuild props / targets. One of the behaviors that the
microbuild props / targets had that wasn't accounted for was the signing
of the VSIX after they are constructed. Hence this lead to signing
errors on insertion.

This PR fixes that by making the following changes:

1. Adds SWIX VSIX to SignToolData.json so they are accounted for during
normal batch signing.
1. Moves the SWIX build to the pre-sign portion of our build.
1. Removes the references from VSMAN -> SWIX. These references are there
only to enforce ordering which is unnecessary. Having them remain risks
that building the VSMAN will cause the SWIX to be re-built which could
possibly invalidate signing.