Cleanup: Use enum for file selection type definitions

Makes it more clear that these belong together and allows using the enum type
rather than just `int`.

source/blender/makesdna/DNA_space_types.h

@@ -698,7 +698,7 @@ typedef struct FileSelectParams {
 
   /* short */
   /** XXXXX for now store type here, should be moved to the operator. */
-  short type;
+  short type; /* eFileSelectType */
   /** Settings for filter, hiding dots files. */
   short flag;
   /** Sort order. */
@@ -807,12 +807,14 @@ enum eFileDetails {
 #define FILE_MAX_LIBEXTRA (FILE_MAX + MAX_ID_NAME)
 
 /* filesel types */
-#define FILE_UNIX 8
-#define FILE_BLENDER 8 /* don't display relative paths */
-#define FILE_SPECIAL 9
+typedef enum eFileSelectType {
+  FILE_LOADLIB = 1,
+  FILE_MAIN = 2,
 
-#define FILE_LOADLIB 1
-#define FILE_MAIN 2
+  FILE_UNIX = 8,
+  FILE_BLENDER = 8, /* don't display relative paths */
+  FILE_SPECIAL = 9,
+} eFileSelectType;
 
 /* filesel op property -> action */
 typedef enum eFileSel_Action {