cgen: support [spawn_stack: 131072] fn attribute, for controlling the max size of the stack, of the spawned threads (#17222)

examples/control_thread_stack_size.v

@@ -0,0 +1,19 @@
+module main
+
+fn main() {
+	th := spawn my_print1()
+	th.wait()
+	th2 := spawn my_print2()
+	th2.wait()
+}
+
+// default stack size
+fn my_print1() {
+	println('hello word')
+}
+
+// 2MB  stack size
+[spawn_stack: 2097152]
+fn my_print2() {
+	println('ahoj svet')
+}