patch 8.2.1478: Vim9: cannot use "true" for some popup options

Problem:    Vim9: cannot use "true" for some popup options.
Solution:   Add dict_get_bool(). (closes #6725)
diff --git a/src/proto/dict.pro b/src/proto/dict.pro
index 093139f..3b66384 100644
--- a/src/proto/dict.pro
+++ b/src/proto/dict.pro
@@ -31,6 +31,7 @@
 varnumber_T dict_get_number(dict_T *d, char_u *key);
 varnumber_T dict_get_number_def(dict_T *d, char_u *key, int def);
 varnumber_T dict_get_number_check(dict_T *d, char_u *key);
+varnumber_T dict_get_bool(dict_T *d, char_u *key, int def);
 char_u *dict2string(typval_T *tv, int copyID, int restore_copyID);
 int eval_dict(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int literal);
 void dict_extend(dict_T *d1, dict_T *d2, char_u *action);