gh-118702: Implement vectorcall for BaseException (#118703)

* BaseException_vectorcall() now creates a tuple from 'args' array.
* Creation an exception using BaseException_vectorcall() is now a
  single function call, rather than having to call
  BaseException_new() and then BaseException_init().
  Calling BaseException_init() is inefficient since it overrides
  the 'args' attribute.
* _PyErr_SetKeyError() now uses PyObject_CallOneArg() to create the
  KeyError instance to use BaseException_vectorcall().