* Instead of always installing the hook but bailing early based on the
configuration, we will instead only install the hook if the
configuration requests it
* Hopefully the updated name should be more clear that we are inhering
some existing cargo artifacts and NOT inheriting something like
CARGO_BUILD_TARGET which refers to the host target being built
* This allows us to copy over the cargo artifacts as early as possible
so that any other phases/hooks (like running clippy) can take
advantage of the cache
* It also avoids installing the artifacts too soon (and making them
older than the source) and having cargo invalidate them
* Rather than clobbering the project's .cargo/config.toml file (if it
exists), the setup hook will update the base configuration used in
$CARGO_HOME/config.toml
* This potentially allows for projects who know what they are doing to
more easily replace their own sources, while falling back to our
configuration
* This will define CARGO_HOME to $PWD/.cargo-home to ensure that cargo
never tries to look for a missing HOME directory as it's default
location
* The hook is also added to `postPatchHooks` (instead of
`preConfigureHooks`) to ensure that it runs before all other
configuration-related hooks
* The intention is to make it more clear that this flag controls copying
the target directory so that *other* derivations can use it, and DOES
NOT control whether we use an *existing* target directory from another
derivation
* If the source root contains a Cargo.lock file it will be used to
create a vendor directory
* Otherwise a (descriptive) error will be thrown describing how to
remediate
* The caller can, of course, manually specify their own `cargoVendorDir`
which will skip the default vendoring
* We can simplify the configuration by removing the
`doCopyTargetToSeparateOutput` parameter
* If a caller wants to copy target artifacts into any other output, it
is pretty trivial for them to add their own logic for it
