Add safe-init test to prevent adding cold elements to hot arrays

This adds a negative test to ensure that the initialization checker does nt allow cold values to be inserted into hot arrays through a method call.

Author: Xavientois

tests/init/neg/cold-insert-hot-array.scala

@@ -0,0 +1,9 @@
+object A:
+ def foo[T](x: T, array: Array[T]): Unit = array(0) = x
+
+class B {
+ var a = new Array[B](2)
+ A.foo(this, a) //error
+ println(a(0).i)
+ val i = 99
+}