refactor(signs): handle non-sign attrs separately (#19784)

src/nvim/sign_defs.h

@@ -33,15 +33,11 @@ struct sign_entry {
 };
 
 /// Sign attributes. Used by the screen refresh routines.
-typedef struct sign_attrs_S {
-  int sat_typenr;
-  char_u *sat_text;
-  int sat_texthl;
-  int sat_linehl;
-  int sat_culhl;
-  int sat_numhl;
-  int sat_prio;  // Used for inserting extmark signs
-} sign_attrs_T;
+typedef struct {
+  char_u *text;
+  int hl_attr_id;
+  int priority;
+} SignTextAttrs;
 
 #define SIGN_SHOW_MAX 9