migration: Add squash schema file to repo

Created by: efritz

This PR adds a fully squashed SQL definition file for each schema into the repo as part of an effort towards #35827.

There's currently some issues around speed that we should address before we land this approach permanently (namely we should do what schemadoc does and just creates a db quickly on your host if it's configured to do so; this is sg, not migrator so we can do shortcuts like that). Fixed by #35869.

Test plan

N/A.