qapi: Fix bullet list markup in documentation

qapi: Fix bullet list markup in documentation

Peter Maydell's commit 100cc4fe0f08 explains:

    rST insists on a blank line before and after a bulleted list [...]
    Add some extra blank lines in the doc comments so they're
    acceptable rST input.

It missed one in qapi/trace.json.

Paolo Bonzini later added another instance in qapi/stats.json,
providing further, if unintended, evidence for his quip that rST is
the Perl of ASCII-based markups.

Both are parsed as ordinary paragraph, resulting in garbled output.

John Snow missed the need for a blank line when converting
docs/devel/qapi-code-gen.txt to rST.

Add the blank lines we need to get the bullet lists recognized as
such.

Kevin Wolf and Lukas Straub added two more, but indented.  Sphinx
recognizes them as (indented) bullet lists.  The indentation looks
slightly off.

Insert a blank line and delete the extra indentation.

Fixes: 100cc4fe0f0827f8da1a5c05f9c65e2aaa40e03d (qapi: Add blank lines before bulleted lists)
Fixes: 467ef823d83e (qmp: add filtering of statistics by target vCPU)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230425064223.820979-10-armbru@redhat.com>
[Fix of docs/devel/qapi-code-gen.rst squashed, commit message adjusted]