filesystem: split const blocks

The rationale for this is that editors / LSP picks up the const comment
and applies it to all members of the block. The root and error
constants are not "permission bits" like the values above them.

Author: djdv

internal/filesystem/filesystem.go

@@ -106,7 +106,9 @@ const (
 	ExecuteUser
 	WriteUser
 	ReadUser
+)
 
+const (
 	Root = "."
 
 	ErrPath     = generic.ConstError("path not valid")