Implement #7818 : Extend rdb$get_context('SYSTEM', '***') with other info from MON$ATTACHMENT

Author: hvlad

doc/sql.extensions/README.context_variables2

@@ -70,10 +70,14 @@ Usage:
    CLIENT_HOST                  | The wire protocol host name of remote client. Value is
                                 | returned for all supported protocols.
                                 |
+   CLIENT_OS_USER               | Remote OS user name
+                                |
    CLIENT_PID                   | Process ID of remote client application
                                 |
    CLIENT_PROCESS               | Process name of remote client application
                                 |
+   CLIENT_VERSION               | Version of the client library used by client application
+                                |
    DB_NAME                      | Canonical name of current database. It is either alias
                                 | name if connectivity via file names is not allowed or
                                 | fully expanded database file name otherwise.

src/jrd/SysFunction.cpp

@@ -379,8 +379,10 @@ const char
 	WIRE_CRYPT_PLUGIN_NAME[] = "WIRE_CRYPT_PLUGIN",
 	CLIENT_ADDRESS_NAME[] = "CLIENT_ADDRESS",
 	CLIENT_HOST_NAME[] = "CLIENT_HOST",
+	CLIENT_OS_USER_NAME[] = "CLIENT_OS_USER",
 	CLIENT_PID_NAME[] = "CLIENT_PID",
 	CLIENT_PROCESS_NAME[] = "CLIENT_PROCESS",
+	CLIENT_VERSION_NAME[] = "CLIENT_VERSION",
 	CURRENT_USER_NAME[] = "CURRENT_USER",
 	CURRENT_ROLE_NAME[] = "CURRENT_ROLE",
 	SESSION_IDLE_TIMEOUT[] = "SESSION_IDLE_TIMEOUT",
@@ -4564,6 +4566,13 @@ dsc* evlGetContext(thread_db* tdbb, const SysFunction*, const NestValueArray& ar
 
 			resultStr = attachment->att_remote_host;
 		}
+		else if (nameStr == CLIENT_OS_USER_NAME)
+		{
+			if (attachment->att_remote_os_user.isEmpty())
+				return NULL;
+
+			resultStr = attachment->att_remote_os_user;
+		}
 		else if (nameStr == CLIENT_PID_NAME)
 		{
 			if (!attachment->att_remote_pid)
@@ -4578,6 +4587,13 @@ dsc* evlGetContext(thread_db* tdbb, const SysFunction*, const NestValueArray& ar
 
 			resultStr = attachment->att_remote_process.ToString();
 		}
+		else if (nameStr == CLIENT_VERSION_NAME)
+		{
+			if (attachment->att_client_version.isEmpty())
+				return NULL;
+
+			resultStr = attachment->att_client_version.ToString();
+		}
 		else if (nameStr == CURRENT_USER_NAME)
 		{
 			const MetaString& user = attachment->getUserName();