Method#unbind clones the method entry, preserving its defined_class.
For methods mixed in via include/extend, defined_class is an ICLASS,
causing UnboundMethod#== to return false when comparing against the
same method obtained via Module#instance_method.

Resolve ICLASS defined_class in method_eq.

[Bug #21873]

https://bugs.ruby-lang.org/issues/21785#note-10
> It is too late to introduce it in Ruby 4.0, let's aim for 4.1.

This reverts commits:

* d0b72429a93e54f1f956b4aedfc25c57dc7001aa
  Add support for signed and unsigned LEB128 to pack/unpack.

* 68a900e30b4ca1537d7975c3a619fd94fca7b084
  add news for pack / unpack directives

This commit adds a new pack format command `R` and `r` for unsigned and
signed LEB128 encoding.  The "r" mnemonic is because this is a
"vaRiable" length encoding scheme.

LEB128 is used in various formats including DWARF, WebAssembly, MQTT,
and Protobuf.

[Feature #21785]

and columns"

This reverts commit 073c4e1cc712064e626914fa4a5a8061f903a637.

https://bugs.ruby-lang.org/issues/6012#note-31
> we will cancel this feature in 4.0 because of design ambiguities
> such as whether to return column positions in bytes or characters as
> in [#21783].

[#21783]: https://bugs.ruby-lang.org/issues/21783

As the markers for spec/mspec/tool/remove_old_guards.rb.

This provides information on the class of the frozen object. It also
results in a much simpler implementation.

Fixes [Bug #21374]

- for non-String argument
- for NUL-contained argument
- for ASCII-incompatible argument

[Bug #21718]

Otherwise objects that don't define it, but define a fairly liberal
`method_missing` method will run into errors that are hard to understand:

```ruby
class Foo
  def method_missing(name, ...)
    name
  end
end

p Foo.new.inspect
```

```
'Kernel#inspect': wrong argument type Symbol (expected Array) (TypeError)
	from ../test.rb:7:in '<main>'
```

`realloc` is not guaranteed to return the same address when shrinking.