patch 8.2.1744: Vim9: using ":const!" is weird

Problem:    Vim9: using ":const!" is weird.
Solution:   Use "var" - "final" - "const" like Dart.  "let" still works for
            now.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index f63ecfc..2f82b8d 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -193,21 +193,21 @@
 enddef
 
 def Test_const()
-  CheckDefFailure(['const var = 234', 'var = 99'], 'E1018:')
-  CheckDefFailure(['const one = 234', 'let one = 99'], 'E1017:')
-  CheckDefFailure(['const list = [1, 2]', 'let list = [3, 4]'], 'E1017:')
-  CheckDefFailure(['const two'], 'E1021:')
-  CheckDefFailure(['const &option'], 'E996:')
+  CheckDefFailure(['final var = 234', 'var = 99'], 'E1018:')
+  CheckDefFailure(['final one = 234', 'let one = 99'], 'E1017:')
+  CheckDefFailure(['final list = [1, 2]', 'let list = [3, 4]'], 'E1017:')
+  CheckDefFailure(['final two'], 'E1125:')
+  CheckDefFailure(['final &option'], 'E996:')
 
   let lines =<< trim END
-    const list = [1, 2, 3]
+    final list = [1, 2, 3]
     list[0] = 4
     list->assert_equal([4, 2, 3])
-    const! other = [5, 6, 7]
+    const other = [5, 6, 7]
     other->assert_equal([5, 6, 7])
 
     let varlist = [7, 8]
-    const! constlist = [1, varlist, 3]
+    const constlist = [1, varlist, 3]
     varlist[0] = 77
     # TODO: does not work yet
     # constlist[1][1] = 88
@@ -216,7 +216,7 @@
     constlist->assert_equal([1, [77, 88], 3])
 
     let vardict = #{five: 5, six: 6}
-    const! constdict = #{one: 1, two: vardict, three: 3}
+    const constdict = #{one: 1, two: vardict, three: 3}
     vardict['five'] = 55
     # TODO: does not work yet
     # constdict['two']['six'] = 66
@@ -229,35 +229,35 @@
 
 def Test_const_bang()
   let lines =<< trim END
-      const! var = 234
+      const var = 234
       var = 99
   END
   CheckDefExecFailure(lines, 'E1018:', 2)
   CheckScriptFailure(['vim9script'] + lines, 'E46:', 3)
 
   lines =<< trim END
-      const! ll = [2, 3, 4]
+      const ll = [2, 3, 4]
       ll[0] = 99
   END
   CheckDefExecFailure(lines, 'E1119:', 2)
   CheckScriptFailure(['vim9script'] + lines, 'E741:', 3)
 
   lines =<< trim END
-      const! ll = [2, 3, 4]
+      const ll = [2, 3, 4]
       ll[3] = 99
   END
   CheckDefExecFailure(lines, 'E1118:', 2)
   CheckScriptFailure(['vim9script'] + lines, 'E684:', 3)
 
   lines =<< trim END
-      const! dd = #{one: 1, two: 2}
+      const dd = #{one: 1, two: 2}
       dd["one"] = 99
   END
   CheckDefExecFailure(lines, 'E1121:', 2)
   CheckScriptFailure(['vim9script'] + lines, 'E741:', 3)
 
   lines =<< trim END
-      const! dd = #{one: 1, two: 2}
+      const dd = #{one: 1, two: 2}
       dd["three"] = 99
   END
   CheckDefExecFailure(lines, 'E1120:')
@@ -2532,6 +2532,12 @@
 def Test_let_declaration_fails()
   let lines =<< trim END
     vim9script
+    final var: string
+  END
+  CheckScriptFailure(lines, 'E1125:')
+
+  lines =<< trim END
+    vim9script
     const var: string
   END
   CheckScriptFailure(lines, 'E1021:')