[lldb] Call __lldb_init_module from __init__

Update `__init__.py` generation to implement `__lldb_init_module`, which calls
`__lldb_init_module` on submodules that define it.

This allows the use case where a user runs `command script import lldb.macosx`.
With this change, the `__lldb_init_module` function in `crashlog.py` and
`heap.py` will be run, which is where command registration is occurring.

Differential Revision: https://reviews.llvm.org/D119179