[lldb] Add some example type anotations to python.swig

[lanza]

Summary

Python3.5 (3.4?) added type annotations to the python language. This
lets tools such as LSPs provide useful IDE-like completion when writing
python.

Add type annotations throughout the python swig API would make writing
lldb python tooling much more approachable for users. This diff is a
first demonstration of the idea.

[labath]

IIUC, this would make the file incompatible with python2, which we still kind of support (though hopefully not for long). This seems like a good idea, but we first need to sort out our py2 story. Given that we've just branched for the 11.0 release, this may actually be a pretty good time to have that disussion, if you would care to start one.

[lanza]

Sounds good, just sent out a message to the mailing list.

lldb/bindings/python.swig

 try:
    import lldbconfig
    _initialize = lldbconfig.INITIALIZE
 except ImportError:
    pass
 debugger_unique_id = 0
 if _initialize:
    SBDebugger.Initialize()
-debugger = None
-target = None
-process = None
-thread = None
-frame = None
+debugger: lldb.SBDebugger = None
+target: lldb.SBTarget = None
+process: lldb.SBProcess = None
+thread: lldb.SBThread = None
+frame: lldb.SBFrame = None
 %}