Don't resolve unqualified types in docstrings using class index (PY-12864)

It may result in false positives where our index-based guess is
incorrect.
MemberInfoBase: use ensureValid
PY-7376 Resolving of relative imports takes into account namespace packages
PY-7378 Add test cases described in issue (problem has been fixed already)
Do not create __init__.py when moving namespace packages
Merge remote-tracking branch 'origin/master'
Snapshot of python-skeletons @ a3175f6
convert to stream: support nested conditions
testdata for IDEA-132725
workaround for opened captures (IDEA-132717)
enum attribute values must be a constant (JLS 9.7.1 IDEA-132747)
new inference: treat array initializer expr as "poly" context
retrieve expected type by containing array creation expression (IDEA-132794)