[LLDB/Lua] call lua_close() on Lua dtor

[LLDB/Lua] call lua_close() on Lua dtor

This patch calls `lua_close()` on Lua dtor.

This guarantees that the Lua GC finalizers are honored, aside from the
usual internal clean up.

It also guarantees a call to the `__close` metamethod of any active
to-be-closed variable in Lua 5.4.

Since the previous `luaL_openlibs()` was a noop, because the standard
library is cached internally, I've removed it.

Differential Revision: https://reviews.llvm.org/D90557