We currently use a script to keep certain duplicate QL files in sync across the repo. For historical reasons, this script has lived in the private repo alongside the rest of CodeQL, even though it's only used for files in the public `ql` repo. This PR moves the script into the public `ql` repo. It is still invoked by Jenkins scripts that live in the private repo during CI, but it can also be invoked directly without having a checkout of the private repo. This is useful for anyone who is modifying the dataflow or IR libraries with only a QL checkout.
We have external users editing queries with Visual Studio, and it seems
to automatically add very specific files to `.gitignore`. These changes
cause conflicts between unrelated PRs.
This commit adds all of `/.vs` to `.gitignore`, which should hopfully
make Visual Studio stop adding more entries.
