sync: add .try_lock() to mutex/rwmutex, add tests (#20381)

vlib/sync/mutex_test.v

@@ -0,0 +1,42 @@
+import sync
+
+struct Counter {
+pub mut:
+	i int
+}
+
+fn write_10000(mut co Counter, mut mx sync.Mutex) {
+	mx.@lock()
+	co.i = 10000
+	mx.unlock()
+}
+
+fn test_mutex() {
+	mut co := &Counter{10086}
+	mut mx := sync.new_mutex()
+	mx.@lock()
+	co.i = 888
+	th := spawn write_10000(mut co, mut mx)
+	mx.unlock() // after mx unlock, thread write_10000 can continue
+	th.wait()
+	mx.destroy()
+	assert co.i == 10000
+}
+
+fn test_try_lock_mutex() {
+	// In Windows, try_lock only avalible after Windows 7
+	$if windows {
+		$if !windows_7 ? {
+			return
+		}
+	}
+	mut mx := sync.new_mutex()
+	mx.@lock()
+	try_fail := mx.try_lock()
+	assert try_fail == false
+	mx.unlock()
+	try_sucess := mx.try_lock()
+	assert try_sucess == true
+	mx.unlock() // you must unlock it, after try_lock sucess
+	mx.destroy()
+}