testing: refactor the v test implementation to make supporting different output modes easier

cmd/tools/modules/testing/output.v

@@ -0,0 +1,40 @@
+module testing
+
+import time
+
+pub enum MessageKind {
+	ok
+	fail
+	skip
+	info
+	sentinel
+}
+
+pub struct LogMessage {
+pub:
+	flow_id string        // the messages of each thread, producing LogMessage, will have all the same unique flowid. Messages by other threads will have other flowid. If you use VJOBS=1 to serialise the execution, then all messages will have the same flowid.
+	file    string        // the _test.v file that the message is about
+	message string        // the actual message text; the result of the event, that the message describes; most reporters could ignore this, since it could be reconstructed by the other fields
+	kind    MessageKind   // see the MessageKind declaration
+	when    time.Time     // when was the message sent (messages are sent by the execution threads at the *end* of each event)
+	took    time.Duration // the duration of the event, that this message describes
+}
+
+pub interface Reporter {
+mut:
+	session_start(message string, mut ts TestSession) // called once per test session, in the main thread, suitable for setting up supporting infrastructure.
+	session_stop(message string, mut ts TestSession) // called once per test session, in the main thread, after everything else, suitable for summaries, creating .xml reports, uploads etc.
+	worker_threads_start(files []string, mut ts TestSession) // called once per test session, in the main thread, right before all the worker threads start
+	worker_threads_finish(mut ts TestSession) // called once per test session, in the main thread, right after all the worker threads finish
+	//
+	report(index int, log_msg LogMessage) // called once per each message, that will be shown (ok/fail/skip etc), only in the reporting thread.
+	report_stop() // called just once after all messages are processed, only in the reporting thread, but before stop_session.
+	//
+	// TODO: reconsider, whether the next methods, should be kept for all reporters, or just moved inside the normal reporter, to simplify the interface
+	progress(index int, message string)
+	update_last_line(index int, message string)
+	update_last_line_and_move_to_next(index int, message string)
+	message(index int, message string)
+	divider() // called to show a long ---------- horizontal line; can be safely ignored in most reporters; used in the main thread.
+	list_of_failed_commands(cmds []string) // called after all testing is done, to produce a small summary that only lists the failed commands, so that they can be retried manually if needed, without forcing the user to scroll and find them.
+}