target: Improve error reporting for CpuModelInfo member @props

target: Improve error reporting for CpuModelInfo member @props

query-cpu-model-comparison, query-cpu-model-baseline, and
query-cpu-model-expansion take CpuModelInfo arguments.  Errors in
@props members of these arguments are reported for 'props', without
further context.  For instance, s390x rejects

    {"execute": "query-cpu-model-comparison", "arguments": {"modela": {"name": "z13", "props": {}}, "modelb": {"name": "z14", "props": []}}}

with

    {"error": {"class": "GenericError", "desc": "Invalid parameter type for 'props', expected: object"}}

This is unusual; the common QAPI unmarshaling machinery would complain
about 'modelb.props'.  Our hand-written code to visit the @props
member neglects to provide the context.

Tweak it so it provides it.  The command above now fails with

    {"error": {"class": "GenericError", "desc": "Invalid parameter type for 'modelb.props', expected: dict"}}

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240305145919.2186971-4-armbru@redhat.com>
Acked-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>