patch 8.2.0640: Vim9: expanding does not work

Problem:    Vim9: expanding  does not work.
Solution:   Find wildcards in not compiled commands.  Reorganize test files.

src/testdir/test_vim9_cmd.vim

@@ -0,0 +1,23 @@
+" Test commands that are not compiled in a :def function
+
+source vim9.vim
+
+def Test_edit_wildcards()
+  let filename = 'Xtest'
+  edit `=filename`
+  assert_equal('Xtest', bufname())
+
+  let filenr = 123
+  edit Xtest`=filenr`
+  assert_equal('Xtest123', bufname())
+
+  filenr = 77
+  edit `=filename``=filenr`
+  assert_equal('Xtest77', bufname())
+
+  edit X`=filename`xx`=filenr`yy
+  assert_equal('XXtestxx77yy', bufname())
+enddef
+
+
+" vim: ts=8 sw=2 sts=2 expandtab tw=80 fdm=marker