bpo-46329: Streamline calling sequence a bit. (GH-31465)

* Move handling of bound-methods to PRECALL.

* Remove call_shape.postcall_shrink

* Remove call_shape.callable

* Remove call_shape.callable. Change CALL oparg to match PRECALL oparg.

* Move KW_NAMES before PRECALL.

* Update opcode docs in dis.rst