Function get_hax_rustc_driver_path

pub(crate) fn get_hax_rustc_driver_path() -> PathBuf

Returns the path to the custom rustc driver used by cargo-hax.

This function retrieves the path of the current executable (i.e. cargo-hax), determines its parent directory, and then appends the driver executable name "driver-hax-frontend-exporter" to it. This path is used to locate the custom rustc driver that computes haxmeta files.