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/dict.c b/src/dict.c
index b351730..01a2eda 100644
--- a/src/dict.c
+++ b/src/dict.c
@@ -703,6 +703,21 @@
 }
 
 /*
+ * Get a bool item (number or true/false) from a dictionary.
+ * Returns "def" if the entry doesn't exist.
+ */
+    varnumber_T
+dict_get_bool(dict_T *d, char_u *key, int def)
+{
+    dictitem_T	*di;
+
+    di = dict_find(d, key, -1);
+    if (di == NULL)
+	return def;
+    return tv_get_bool(&di->di_tv);
+}
+
+/*
  * Return an allocated string with the string representation of a Dictionary.
  * May return NULL.
  */