file_util: Use an enum class for GetUserPath()

Instead of using an unsigned int as a parameter and expecting a user to
always pass in the correct values, we can just convert the enum into an
enum class and use that type as the parameter type instead, which makes
the interface more type safe.

We also get rid of the bookkeeping "NUM_" element in the enum by just
using an unordered map. This function is generally low-frequency in
terms of calls (and I'd hope so, considering otherwise would mean we're
slamming the disk with IO all the time) so I'd consider this acceptable
in this case.

src/common/file_util.h

@@ -17,21 +17,20 @@
 #include "common/string_util.h"
 #endif
 
-// User directory indices for GetUserPath
-enum {
-    D_USER_IDX,
-    D_ROOT_IDX,
-    D_CONFIG_IDX,
-    D_CACHE_IDX,
-    D_SDMC_IDX,
-    D_NAND_IDX,
-    D_SYSDATA_IDX,
-    D_LOGS_IDX,
-    NUM_PATH_INDICES
-};
-
 namespace FileUtil {
 
+// User paths for GetUserPath
+enum class UserPath {
+    CacheDir,
+    ConfigDir,
+    LogDir,
+    NANDDir,
+    RootDir,
+    SDMCDir,
+    SysDataDir,
+    UserDir,
+};
+
 // FileSystem tree node/
 struct FSTEntry {
     bool isDirectory;
@@ -124,7 +123,7 @@ bool SetCurrentDir(const std::string& directory);
 
 // Returns a pointer to a string with a Citra data dir in the user's home
 // directory. To be used in "multi-user" mode (that is, installed).
-const std::string& GetUserPath(const unsigned int DirIDX, const std::string& newPath = "");
+const std::string& GetUserPath(UserPath path, const std::string& new_path = "");
 
 // Returns the path to where the sys file are
 std::string GetSysDirectory();