patch 8.2.1306: checking for first character of dict key is inconsistent

Problem:    Checking for first character of dict key is inconsistent.
Solution:   Add eval_isdictc(). (closes #6546)
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 8efb1f6..1ed3211 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -3758,7 +3758,7 @@
 	    if (next != NULL &&
 		    ((next[0] == '-' && next[1] == '>'
 				 && (next[2] == '{' || ASCII_ISALPHA(next[2])))
-		    || (next[0] == '.' && ASCII_ISALPHA(next[1]))))
+		    || (next[0] == '.' && eval_isdictc(next[1]))))
 	    {
 		next = next_line_from_context(cctx, TRUE);
 		if (next == NULL)
@@ -3922,7 +3922,7 @@
 		return FAIL;
 	    // dictionary member: dict.name
 	    p = *arg;
-	    if (eval_isnamec1(*p))
+	    if (eval_isdictc(*p))
 		while (eval_isnamec(*p))
 		    MB_PTR_ADV(p);
 	    if (p == *arg)