Fixes mypyc/mypyc#1245.

This builds on #22163 and uses its helpers, so the first commit here is that PR. Only the second commit
is new.

A class decorated with @deprecated("...") (PEP 702) is compiled as a non-native class, because deprecated isn't one of the class decorators that native classes support. Nothing reports this, and the class gets much slower: 213 ns instead of 17 ns per iteration for a method call and an attribute read in a compiled loop.

Calling the runtime decorator on a native class can't work, since it replaces __new__ on the class. With this PR mypyc doesn't call it. The class stays native and does itself what the decorator would arrange:

• __deprecated__ is set on the class.
• Creating an instance of the class itself (not of a subclass) issues the warning, before __new__ or
  __init__ run. This is done in the native constructor and in tp_new. A class with a built-in base
  class (an exception, for example) gets a tp_new for this, since it otherwise inherits it.
• Creating a subclass issues the warning. The class gets an __init_subclass__ that warns and calls the
  next one. If the class defines __init_subclass__, the warning is compiled into that method instead,
  with the mechanism from [mypyc] Support @deprecated on functions and methods #22163.