Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2020-10-10' into staging

QAPI patches patches for 2020-10-10

# gpg: Signature made Sat 10 Oct 2020 10:43:14 BST
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2020-10-10: (34 commits)
  qapi/visit.py: add type hint annotations
  qapi/visit.py: remove unused parameters from gen_visit_object
  qapi/visit.py: assert tag_member contains a QAPISchemaEnumType
  qapi/types.py: remove one-letter variables
  qapi/types.py: add type hint annotations
  qapi/gen.py: delint with pylint
  qapi/gen.py: update write() to be more idiomatic
  qapi/gen.py: Remove unused parameter
  qapi/gen.py: add type hint annotations
  qapi/gen: Make _is_user_module() return bool
  qapi/source.py: delint with pylint
  qapi/source.py: add type hint annotations
  qapi/commands.py: add type hint annotations
  qapi/commands.py: Don't re-bind to variable of different type
  qapi/events.py: Move comments into docstrings
  qapi/events.py: add type hint annotations
  qapi: establish mypy type-checking baseline
  qapi/common.py: move build_params into gen.py
  qapi/common.py: Convert comments into docstrings, and elaborate
  qapi/common.py: add type hint annotations
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>