Some of the scripts in scripts/ci were not reliable detecting the path
they were operating in. Additionally the deno_tests script was not
correctly picking up the ROOT_MODULE environment variable. Add more
robust path handling and fix the deno_tests script.
After some discussion with PVH I realise that the repo structure in the
last reorg was very rust-centric. In an attempt to put each language on
a level footing move the rust code and project files into ./rust
For larger rust projects it's common to put all rust code in a directory
called `crates`. This helps in general by reducing the number of
directories in the top level but it's particularly helpful for us
because some directories _do not_ contain Rust code. In particular
`automerge-js`. Move rust code into `/crates` to make the repo easier
to navigate.
