The return value of Module#set_temporary_name was changed
to return `self`, but the existing tests
did not verify this.

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

Fixes [Bug #21374]

The test is no longer useful since
5c7dfe85a1dc49334e2828791f0ade42eee662db because Module#initialize_copy
is empty/not defined anymore.

Previously, you could override the class initialize_dup/initialize_clone
method and the class hierarchy would not be set correctly inside the
method before calling super.

This removes Module#initialize_copy, and instead makes Object#dup/clone
call the underlying C function (rb_mod_init_copy) before calling the
appropriate initialize_dup/initialize_clone method.

This results in the following fixes:

* The appropriate initialize_dup method is called (dup on a class
  will respect superclass initialize_dup).

* Inside class initialize_dup/initialize_clone/initialize_copy,
  class ancestor hierarchy is correct.

* Calling singleton_class inside initialize_dup no longer raises
  a TypeError later in dup.

* Calling singleton_class.ancestors inside initialize_dup no
  longer results in missing ancestors.

Fixes [Bug #21538]

On systems where the Encoding.default_internal defaults to US-ASCII instead
of UTF-8, some tests using assert_raise_with_message can fail since it no
longer changes Encoding.default_internal in 79f5202.

This tests explicitly uses EnvUtil.with_default_internal on systems where
these tests fail.