Fix crash when allocating classes with newobj hook

	We need to zero out the whole slot when running the newobj hook for a
	newly allocated class because the slot could be filled with garbage,
	which would cause a crash if a GC runs inside of the newobj hook.

	For example, the following script crashes:

	```
	require "objspace"

	GC.stress = true

	ObjectSpace.trace_object_allocations {
	  100.times do
	    Class.new
	  end
	}
	```

	[Bug #19482]
	---
	 gc.c                           | 8 +++++++-
	 test/objspace/test_objspace.rb | 7 +++++++
	 2 files changed, 14 insertions(+), 1 deletion(-)

	Fix interpreter crash caused by RUBY_INTERNAL_EVENT_NEWOBJ + Ractors

	When a Ractor is created whilst a tracepoint for
	RUBY_INTERNAL_EVENT_NEWOBJ is active, the interpreter crashes. This is
	because during the early setup of the Ractor, the stdio objects are
	created, which allocates Ruby objects, which fires the tracepoint.
	However, the tracepoint machinery tries to dereference the control frame
	(ec->cfp->pc), which isn't set up yet and so crashes with a null pointer
	dereference.

	Fix this by not firing GC tracepoints if cfp isn't yet set up.
	---
	 gc.c                         |  1 +
	 test/objspace/test_ractor.rb | 17 +++++++++++++++++
	 2 files changed, 18 insertions(+)
	 create mode 100644 test/objspace/test_ractor.rb

I see several arguments in doing so.

First they use a non trivial amount of memory, so for various memory
profiling/mapping tools it is relevant to have visibility of the space
occupied by shapes.

Then, some pathological code can create a tons of shape, so it is
valuable to have a way to have a way to observe shapes without having
to compile Ruby with `SHAPE_DEBUG=1`.

And additionally it's likely much faster to dump then this way than
to use `RubyVM::Shape`.

There are however a few open questions:

- Shapes can't respect the `since:` argument. Not sure what to do when
  it is provided. Would probably make sense to not dump them.
- Maybe it would make more sense to have a separate `ObjectSpace.dump_shapes`?
- Maybe instead `dump_all` should take a `shapes: false` argument?

Additionally, `ObjectSpace.dump_shapes` is added for the use case of
debugging the evolution of the shape tree.

This commit adds RVALUE_OVERHEAD for storing metadata at the end of the
slot. This commit moves the ractor_belonging_id in debug builds from the
flags to RVALUE_OVERHEAD which frees the 16 bits in the headers for
object shapes.

This commit adds a `capacity` field to shapes, and adds shape
transitions whenever an object's capacity changes. Objects which are
allocated out of a bigger size pool will also make a transition from the
root shape to the shape with the correct capacity for their size pool
when they are allocated.

This commit will allow us to remove numiv from objects completely, and
will also mean we can guarantee that if two objects share shapes, their
IVs are in the same positions (an embedded and extended object cannot
share shapes). This will enable us to implement ivar sets in YJIT using
object shapes.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>

This patch pushes dummy frames when loading code for the
profiling purpose.

The following methods push a dummy frame:
* `Kernel#require`
* `Kernel#load`
* `RubyVM::InstructionSequence.compile_file`
* `RubyVM::InstructionSequence.load_from_binary`

https://bugs.ruby-lang.org/issues/18559

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>

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