unc - implement validation (microsoft#182286)

Author: bpasero

src/vs/workbench/browser/workbench.contribution.ts

@@ -696,7 +696,9 @@ const registry = Registry.as<IConfigurationRegistry>(ConfigurationExtensions.Con
 			'security.allowedUNCHosts': {
 				'type': 'array',
 				'items': {
-					'type': 'string'
+					'type': 'string',
+					'pattern': '^[^\\\\]+$',
+					'patternErrorMessage': localize('security.allowedUNCHosts.patternErrorMessage', 'UNC host names must not contain backslashes.')
 				},
 				'default': [],
 				'markdownDescription': localize('security.allowedUNCHosts', 'A set of UNC host names (without leading or trailing backslash, for example `192.168.0.1` or `my-server`) to allow without user confirmation. If a UNC host is being accessed that is not allowed via this setting or has not been acknowledged via user confirmation, an error will occur and the operation stopped. A restart is required when changing this setting. Find out more about this setting at https://aka.ms/vscode-windows-unc.'),