89cfc152071 made this event dispatch to pass `Qundef`
to user defined callback method by mistake.
This commit fix it to be `nil`.

Introduce another semantic value stack for Ripper so that
Ripper can manage both Node and Ruby Object separately.
This rearchitectutre of Ripper solves these issues.
Therefore adding test cases for them.

* [Bug 10436] https://bugs.ruby-lang.org/issues/10436
* [Bug 18988] https://bugs.ruby-lang.org/issues/18988
* [Bug 20055] https://bugs.ruby-lang.org/issues/20055

Checked the differences of `Ripper.sexp` for files under `/test/ruby`
are only on test_pattern_matching.rb.
The differences comes from the differences between
`new_hash_pattern_tail` functions between parser and Ripper.
Ripper `new_hash_pattern_tail` didn’t call `assignable` then
`kw_rest_arg` wasn’t marked as local variable.
This is also fixed by this commit.

```
--- a/./tmp/before/test_pattern_matching.rb
+++ b/./tmp/after/test_pattern_matching.rb
@@ -3607,7 +3607,7 @@
                  [:in,
                   [:hshptn, nil, [], [:var_field, [:@ident, “a”, [984, 13]]]],
                   [[:binary,
-                    [:vcall, [:@ident, “a”, [985, 10]]],
+                    [:var_ref, [:@ident, “a”, [985, 10]]],
                     :==,
                     [:hash, nil]]],
                   nil]]],
@@ -3662,7 +3662,7 @@
                  [:in,
                   [:hshptn, nil, [], [:var_field, [:@ident, “a”, [993, 13]]]],
                   [[:binary,
-                    [:vcall, [:@ident, “a”, [994, 10]]],
+                    [:var_ref, [:@ident, “a”, [994, 10]]],
                     :==,
                     [:hash,
                      [:assoclist_from_args,
@@ -3813,7 +3813,7 @@
                    [:command,
                     [:@ident, “raise”, [1022, 10]],
                     [:args_add_block,
-                     [[:vcall, [:@ident, “b”, [1022, 16]]]],
+                     [[:var_ref, [:@ident, “b”, [1022, 16]]]],
                      false]]],
                   [:else, [[:var_ref, [:@kw, “true”, [1024, 10]]]]]]]],
                nil,
@@ -3876,7 +3876,7 @@
                      [:@int, “0”, [1033, 15]]],
                     :“&&“,
                     [:binary,
-                     [:vcall, [:@ident, “b”, [1033, 20]]],
+                     [:var_ref, [:@ident, “b”, [1033, 20]]],
                      :==,
                      [:hash, nil]]]],
                   nil]]],
@@ -3946,7 +3946,7 @@
                      [:@int, “0”, [1042, 15]]],
                     :“&&“,
                     [:binary,
-                     [:vcall, [:@ident, “b”, [1042, 20]]],
+                     [:var_ref, [:@ident, “b”, [1042, 20]]],
                      :==,
                      [:hash,
                       [:assoclist_from_args,
@@ -5206,7 +5206,7 @@
                      [[:assoc_new,
                        [:@label, “c:“, [1352, 22]],
                        [:@int, “0”, [1352, 25]]]]]],
-                   [:vcall, [:@ident, “r”, [1352, 29]]]],
+                   [:var_ref, [:@ident, “r”, [1352, 29]]]],
                   false]]],
                [:binary,
                 [:call,
@@ -5299,7 +5299,7 @@
                       [:assoc_new,
                        [:@label, “c:“, [1367, 34]],
                        [:@int, “0”, [1367, 37]]]]]],
-                   [:vcall, [:@ident, “r”, [1367, 41]]]],
+                   [:var_ref, [:@ident, “r”, [1367, 41]]]],
                   false]]],
                [:binary,
                 [:call,
@@ -5931,7 +5931,7 @@
              [:in,
               [:hshptn, nil, [], [:var_field, [:@ident, “r”, [1533, 11]]]],
               [[:binary,
-                [:vcall, [:@ident, “r”, [1534, 8]]],
+                [:var_ref, [:@ident, “r”, [1534, 8]]],
                 :==,
                 [:hash,
                  [:assoclist_from_args,
```

After 6c0925ba7017efde6091e2ec4f1a6be268166696, it was impossible
to distinguish between the presence or absence of `*`.

    # Before the commit
    Ripper.sexp('0 in []')[1][0][2][1]  #=> [:aryptn, nil, nil, nil, nil]
    Ripper.sexp('0 in [*]')[1][0][2][1] #=> [:aryptn, nil, nil, [:var_field, nil], nil]

    # After the commit
    Ripper.sexp('0 in []')[1][0][2][1]  #=> [:aryptn, nil, nil, nil, nil]
    Ripper.sexp('0 in [*]')[1][0][2][1] #=> [:aryptn, nil, nil, nil, nil]

This commit reverts it.

It should also check for duplicate names.

This commit is based on the patch by @nobu.

Implements [Feature #17276]

[Feature #17260] One-line pattern matching using tASSOC

R-assignment is rejected instead.