Function to access (and manage) the depmap package cache. `dmCache()` returns the central `depmap` cache.
Details
The cache is an object of class `BiocFileCache`, and created with [BiocFileCache::BiocFileCache()]. It can be either the package-wide cache as defined by `dmCache()` or an instaned provided by the user.
When projects are cached, they are given a resource name (`rname`), that is set to the file's identifier.