Fetching from CMake removes the need for installing Corrosion entirely.
Not only this makes it easier to build with chronik, but it also makes it easier
to maintain and bump the versions as it is now all in a single place.
Note that the Rust_CARGO_TARGET variable needs to be recomputed from the various
variables set by corrosion using this method:
https://corrosion-rs.github.io/corrosion/v0.4/usage.html#information-provided-by-corrosion
While I'm touching the file, I also fixed the dependency name for generating the bridge c++ files: chronik-lib-static is a name that is set internally by Corrosion and is not documented, but the property is actually documented and retrieving the name from here will be more reliable.
Depends on D15506.