9pfs: deprecate 'proxy' backend

As recent CVE-2023-2861 (fixed by f6b0de53fb) once again showed, the 9p
'proxy' fs driver is in bad shape. Using the 'proxy' backend was already
discouraged for safety reasons before and we recommended to use the
'local' backend (preferably in conjunction with its 'mapped' security
model) instead, but now it is time to officially deprecate the 'proxy'
backend.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1qDkmw-0007M1-8f@lizzy.crudebyte.com>

meson.build

@@ -4179,7 +4179,7 @@ if have_block
   summary_info += {'Block whitelist (ro)': get_option('block_drv_ro_whitelist')}
   summary_info += {'Use block whitelist in tools': get_option('block_drv_whitelist_in_tools')}
   summary_info += {'VirtFS (9P) support':    have_virtfs}
-  summary_info += {'VirtFS (9P) Proxy Helper support': have_virtfs_proxy_helper}
+  summary_info += {'VirtFS (9P) Proxy Helper support (deprecated)': have_virtfs_proxy_helper}
   summary_info += {'Live block migration': config_host_data.get('CONFIG_LIVE_BLOCK_MIGRATION')}
   summary_info += {'replication support': config_host_data.get('CONFIG_REPLICATION')}
   summary_info += {'bochs support':     get_option('bochs').allowed()}