patch 8.2.2204: Vim9: using -> both for method and lambda is confusing

Problem:    Vim9: using -> both for method and lambda is confusing.
Solution:   Use => for lambda in :def function.

src/testdir/test_vim9_expr.vim

@@ -1887,6 +1887,100 @@ def Test_expr7_lambda()
   CheckDefFailure(['var Fx = {a -> [0', ' 1]}'], 'E696:', 2)
 enddef
 
+def NewLambdaWithComments(): func
+  return (x) =>
+            # some comment
+            x == 1
+            # some comment
+            ||
+            x == 2
+enddef
+
+def NewLambdaUsingArg(x: number): func
+  return () =>
+            # some comment
+            x == 1
+            # some comment
+            ||
+            x == 2
+enddef
+
+def Test_expr7_new_lambda()
+  var lines =<< trim END
+      var La = () => 'result'
+      assert_equal('result', La())
+      assert_equal([1, 3, 5], [1, 2, 3]->map((key, val) => key + val))
+
+      # line continuation inside lambda with "cond ? expr : expr" works
+      var ll = range(3)
+      map(ll, (k, v) => v % 2 ? {
+                ['111']: 111 } : {}
+            )
+      assert_equal([{}, {111: 111}, {}], ll)
+
+      ll = range(3)
+      map(ll, (k, v) => v == 8 || v
+                    == 9
+                    || v % 2 ? 111 : 222
+            )
+      assert_equal([222, 111, 222], ll)
+
+      ll = range(3)
+      map(ll, (k, v) => v != 8 && v
+                    != 9
+                    && v % 2 == 0 ? 111 : 222
+            )
+      assert_equal([111, 222, 111], ll)
+
+      var dl = [{key: 0}, {key: 22}]->filter(( _, v) => v['key'] )
+      assert_equal([{key: 22}], dl)
+
+      dl = [{key: 12}, {['foo']: 34}]
+      assert_equal([{key: 12}], filter(dl,
+            (_, v) => has_key(v, 'key') ? v['key'] == 12 : 0))
+
+      assert_equal(false, NewLambdaWithComments()(0))
+      assert_equal(true, NewLambdaWithComments()(1))
+      assert_equal(true, NewLambdaWithComments()(2))
+      assert_equal(false, NewLambdaWithComments()(3))
+
+      assert_equal(false, NewLambdaUsingArg(0)())
+      assert_equal(true, NewLambdaUsingArg(1)())
+
+      var res = map([1, 2, 3], (i: number, v: number) => i + v)
+      assert_equal([1, 3, 5], res)
+
+      # Lambda returning a dict
+      var Lmb = () => {key: 42}
+      assert_equal({key: 42}, Lmb())
+  END
+  CheckDefSuccess(lines)
+
+  CheckDefFailure(["var Ref = (a)=>a + 1"], 'E1001:')
+  CheckDefFailure(["var Ref = (a)=> a + 1"], 'E1001:')
+  CheckDefFailure(["var Ref = (a) =>a + 1"], 'E1001:')
+
+  CheckDefFailure(["filter([1, 2], (k,v) => 1)"], 'E1069:', 1)
+  # error is in first line of the lambda
+  CheckDefFailure(["var L = (a) -> a + b"], 'E1001:', 1)
+
+# TODO: lambda after -> doesn't work yet
+#  assert_equal('xxxyyy', 'xxx'->((a, b) => a .. b)('yyy'))
+
+#  CheckDefExecFailure(["var s = 'asdf'->{a -> a}('x')"],
+#        'E1106: One argument too many')
+#  CheckDefExecFailure(["var s = 'asdf'->{a -> a}('x', 'y')"],
+#        'E1106: 2 arguments too many')
+#  CheckDefFailure(["echo 'asdf'->{a -> a}(x)"], 'E1001:', 1)
+
+  CheckDefSuccess(['var Fx = (a) => {k1: 0,', ' k2: 1}'])
+  CheckDefFailure(['var Fx = (a) => {k1: 0', ' k2: 1}'], 'E722:', 2)
+  CheckDefFailure(['var Fx = (a) => {k1: 0,', ' k2 1}'], 'E720:', 2)
+
+  CheckDefSuccess(['var Fx = (a) => [0,', ' 1]'])
+  CheckDefFailure(['var Fx = (a) => [0', ' 1]'], 'E696:', 2)
+enddef
+
 def Test_expr7_lambda_vim9script()
   var lines =<< trim END
       vim9script