Add a function to DirAccess to check which access the path belongs to.

[shutaozhenzhen]

I want to check path input by user. Now I can use DirAccess.dir_exists_absolute to check if this path is a valid path. But I also want to know which access this path belongs to.

[AThousandShips]

The specific access would be based on if it's prefixed with user:// or res:// I'd say, I don't think the global path for either of these should be treated as being in a specific access when accessed by a global path

[shutaozhenzhen]

yes, but this need to do char check, I think it is better to have a simple func

[AThousandShips]

If it's just a matter of checking the prefix that makes sense, but that's also so simple that I don't think it's reasonable to add a new feature when it's as simple as using existing methods