Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2022-01-27-v2' into staging

QAPI patches patches for 2022-01-27

# gpg: Signature made Thu 27 Jan 2022 14:19:51 GMT
# 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-2022-01-27-v2:
  qapi: generate trace events by default
  meson: document why we don't generate trace events for tests/ and qga/
  docs/qapi-code-gen: update to cover trace events code generation
  meson: generate trace events for qmp commands
  qapi/commands: Optionally generate trace for QMP commands
  qapi/commands: refactor error handling code
  qapi/gen: Add FOO.trace-events output module
  schemas: add missing vim modeline

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