[lldb] Update some uses of Python2 API in typemaps.

Python 3 doesn't have a distinction between PyInt and PyLong, it's all
PyLong now.

This also fixes a bug in SetNumberFromObject. This used to crash LLDB:
```
lldb -o "script data=lldb.SBData(); data.SetDataFromUInt64Array([2**63])"
```

The problem happened in the PyInt path:
```
  if (PyInt_Check(obj))
      number = static_cast<T>(PyInt_AsLong(obj));
```
when obj doesn't fit in a signed long, `PyInt_AsLong` would fail with
"OverflowError: Python int too large to convert to C long".

The existing long path does the right thing, as it will call
`PyLong_AsUnsignedLongLong` for uint64_t.

Differential Revision: https://reviews.llvm.org/D146590