patch 8.2.1322: Vim9: method on double quoted string doesn't work

Problem:    Vim9: method on double quoted string doesn't work.
Solution:   Recognize double quoted string. (closes #6562)

src/ex_docmd.c

@@ -3277,7 +3277,7 @@ find_ex_command(
 	char_u *pskip = (*eap->cmd == '&' || *eap->cmd == '$'
 				|| *eap->cmd == '@') ? eap->cmd + 1 : eap->cmd;
 
-	if (vim_strchr((char_u *)"{('[", *p) != NULL
+	if (vim_strchr((char_u *)"{('[\"", *p) != NULL
 	       || ((p = to_name_const_end(pskip)) > eap->cmd && *p != NUL))
 	{
 	    int oplen;
@@ -3293,6 +3293,8 @@ find_ex_command(
 			    *eap->cmd == '{'
 			    // "'string'->func()" is an expression.
 			 || *eap->cmd == '\''
+			    // '"string"->func()' is an expression.
+			 || *eap->cmd == '"'
 			    // "g:varname" is an expression.
 			 || eap->cmd[1] == ':'
 			    )

src/testdir/test_vim9_expr.vim

@@ -1638,8 +1638,9 @@ enddef
 def Test_expr7_method_call()
   new
   setline(1, ['first', 'last'])
-  eval 'second'->append(1)
-  assert_equal(['first', 'second', 'last'], getline(1, '$'))
+  'second'->append(1)
+  "third"->append(2)
+  assert_equal(['first', 'second', 'third', 'last'], getline(1, '$'))
   bwipe!
 
   let bufnr = bufnr()

src/testdir/test_vim9_func.vim

@@ -502,8 +502,11 @@ def Test_vim9script_call()
     assert_equal('some', var)
 
     # line starting with single quote is not a mark
+    # line starting with double quote can be a method call
     'asdfasdf'->MyFunc()
     assert_equal('asdfasdf', var)
+    "xyz"->MyFunc()
+    assert_equal('xyz', var)
 
     def UseString()
       'xyork'->MyFunc()
@@ -511,6 +514,12 @@ def Test_vim9script_call()
     UseString()
     assert_equal('xyork', var)
 
+    def UseString2()
+      "knife"->MyFunc()
+    enddef
+    UseString2()
+    assert_equal('knife', var)
+
     # prepending a colon makes it a mark
     new
     setline(1, ['aaa', 'bbb', 'ccc'])

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1322,
 /**/
     1321,
 /**/