bpo-33325: Optimize sequences of constants in the compiler

[serhiy-storchaka]

• Replace LOAD_CONST c1, LOAD_CONST c2, ... LOAD_CONST cn, BUILD_LIST n
  with LOAD_CONST (c1, c2, ... cn), BUILD_LIST_UNPACK 1.

• Replace LOAD_CONST c1, LOAD_CONST c2, ... LOAD_CONST cn, BUILD_SET n
  with LOAD_CONST frozenset({c1, c2, ... cn}), BUILD_SET_UNPACK 1.

• Replace LOAD_CONST c1, LOAD_CONST c2, ... LOAD_CONST cn
  with LOAD_CONST (c1, c2, ... cn), UNPACK_SEQUENCE n.

• Remove unused constants.

https://bugs.python.org/issue33325

[serhiy-storchaka]

Closed because in practice the benefit is very small and not stable.