tools, examples: add --only-watch=*.v option to v watch (#18974)

examples/vwatch/cli_clock/main.v

@@ -0,0 +1,14 @@
+import time
+// This example demonstrates how to use `v watch` for simple CLI apps.
+
+fn main() {
+	println('Run with: `v watch run examples/vwatch/cli_clock`,')
+	println('then modify timer.v in your editor.')
+	println('The application will be restarted,')
+	println('as soon as you save your changes.')
+	println('')
+	for {
+		println('The time is now: ${time.now()}')
+		time.sleep(1000 * time.millisecond)
+	}
+}