Eagerly name modules and classes
Eagerly name modules and classes

* variable.c: make the hidden ivars `classpath` and `tmp_classpath` the source
  of truth for module and constant names. Assign to them when modules are bind
  to constants.

* variable.c: remove references to module name cache, as what used to be the cache
  is now the source of truth. Remove rb_class_path_no_cache().

* variable.c: remove the hidden ivar `classid`. This existed for the purposes of
  module name search, which is now replaced. Also, remove the associated
  rb_name_class().

* class.c: use rb_set_class_path_string to set the name of Object during boot.
  Must use a fstring as this runs before rb_cString is initialized and
  creating a normal string leads to a VALUE without a class.

* spec/ruby/core/module/name_spec.rb: add a few specs to specify what happens
  to Module#name across multiple operations. These specs pass without other
  code changes in this commit.

[Feature #15765]

nobu/rubyspec,nobu/rubyspec,nobu/rubyspec,eregon/rubyspec,ruby/spec,ruby/spec,eregon/rubyspec,eregon/rubyspec,ruby/spec