Node has not been managed by GC from Ruby 2.5.
Therefore these codes are not needed. If ObjectSpace depends on Node,
it needs to update the file when node type is updated. Delete node
related codes to avoid such update.

This node type was added for the multi-value experiment back in 2004.
The feature itself was removed after a few years, but this is its
remnant.

All kind of AST nodes use same struct RNode, which has u1, u2, u3 union members
for holding different kind of data.
This has two problems.

1. Low flexibility of data structure

Some nodes, for example NODE_TRUE, don’t use u1, u2, u3. On the other hand,
NODE_OP_ASGN2 needs more than three union members. However they use same
structure definition, need to allocate three union members for NODE_TRUE and
need to separate NODE_OP_ASGN2 into another node.
This change removes the restriction so make it possible to
change data structure by each node type.

2. No compile time check for union member access

It’s developer’s responsibility for using correct member for each node type when it’s union.
This change clarifies which node has which type of fields and enables compile time check.

This commit also changes node_buffer_elem_struct buf management to handle
different size data with alignment.

[Feature #19425]

By this change, syntax error is recovered smaller units.
In the case below, "DEFN :bar" is same level with "CLASS :Foo"
now.

```
module Z
  class Foo
    foo.
  end

  def bar
  end
end
```

[Feature #19013]

Revert "* expand tabs. [ci skip]"

This reverts commit 830b5b5c351c5c6efa5ad461ae4ec5085e5f0275.

Revert "This commit implements the Object Shapes technique in CRuby."

This reverts commit 9ddfd2ca004d1952be79cf1b84c52c79a55978f4.

Object Shapes is used for accessing instance variables and representing the
"frozenness" of objects.  Object instances have a "shape" and the shape
represents some attributes of the object (currently which instance variables are
set and the "frozenness").  Shapes form a tree data structure, and when a new
instance variable is set on an object, that object "transitions" to a new shape
in the shape tree.  Each shape has an ID that is used for caching. The shape
structure is independent of class, so objects of different types can have the
same shape.

For example:

```ruby
class Foo
  def initialize
    # Starts with shape id 0
    @a = 1 # transitions to shape id 1
    @b = 1 # transitions to shape id 2
  end
end

class Bar
  def initialize
    # Starts with shape id 0
    @a = 1 # transitions to shape id 1
    @b = 1 # transitions to shape id 2
  end
end

foo = Foo.new # `foo` has shape id 2
bar = Bar.new # `bar` has shape id 2
```

Both `foo` and `bar` instances have the same shape because they both set
instance variables of the same name in the same order.

This technique can help to improve inline cache hits as well as generate more
efficient machine code in JIT compilers.

This commit also adds some methods for debugging shapes on objects.  See
`RubyVM::Shape` for more details.

For more context on Object Shapes, see [Feature: #18776]

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: Eileen M. Uchitelle <eileencodes@gmail.com>
Co-Authored-By: John Hawthorn <john@hawthorn.email>