Add a unit test for lifetime dependence

Author: meg-gupta

test/Sema/explicit_lifetime_dependence_specifiers2.swift

@@ -12,9 +12,14 @@ struct AnotherBufferView : ~Escapable, _BitwiseCopyable {
 
 struct BufferView : ~Escapable {
   let ptr: UnsafeRawBufferPointer
-  init(_ bv: borrowing AnotherBufferView) -> _borrow(bv) Self {
+  init(_ bv: borrowing AnotherBufferView) -> dependsOn(bv) Self {
     self.ptr = bv.ptr
     return self
   }
 }
 
+struct NonescapableType: ~Escapable {}
+
+func f<T: ~Escapable & _BitwiseCopyable>(arg: T) -> NonescapableType {
+  NonescapableType()
+}