patch 8.2.4697: Vim9: crash when adding a duplicate key to a dictionary

Problem:    Vim9: crash when adding a duplicate key to a dictionary.
Solution:   Clear the stack item when it has been moved into the dictionary.
            (closes #10087)

src/testdir/test_vim9_expr.vim

@@ -2774,6 +2774,9 @@ def Test_expr8_dict()
   v9.CheckScriptFailure(['vim9script', "var x = {xxx: 1,"], 'E723:', 2)
   v9.CheckDefAndScriptFailure(["var x = {['a']: xxx}"], ['E1001:', 'E121:'], 1)
   v9.CheckDefAndScriptFailure(["var x = {a: 1, a: 2}"], 'E721:', 1)
+  g:key = 'x'
+  v9.CheckDefExecAndScriptFailure(["var x = {[g:key]: 'text', [g:key]: 'text'}"], 'E721:', 1)
+  unlet g:key
   v9.CheckDefExecAndScriptFailure(["var x = g:anint.member"], ['E715:', 'E488:'], 1)
   v9.CheckDefExecAndScriptFailure(["var x = g:dict_empty.member"], 'E716:', 1)
 

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4697,
 /**/
     4696,
 /**/

src/vim9execute.c

@@ -196,8 +196,10 @@ exe_newdict(int count, ectx_T *ectx)
 		dict_unref(dict);
 		return FAIL;
 	    }
-	    item->di_tv = *STACK_TV_BOT(2 * (idx - count) + 1);
+	    tv = STACK_TV_BOT(2 * (idx - count) + 1);
+	    item->di_tv = *tv;
 	    item->di_tv.v_lock = 0;
+	    tv->v_type = VAR_UNKNOWN;
 	    if (dict_add(dict, item) == FAIL)
 	    {
 		// can this ever happen?
@@ -5363,7 +5365,7 @@ call_def_function(
     did_emsg_def += save_did_emsg_def;
 
 failed_early:
-    // Free all local variables, but not arguments.
+    // Free all arguments and local variables.
     for (idx = 0; idx < ectx.ec_stack.ga_len; ++idx)
 	clear_tv(STACK_TV(idx));
     ex_nesting_level = orig_nesting_level;