Revert property wrapper synthesis change

Author: phausler

test/decl/var/property_wrappers_synthesis.swift

@@ -51,7 +51,7 @@ struct UseWillSetDidSet {
 }
 
 @propertyWrapper
-struct ObservableWrapper<Value> {
+struct Observable<Value> {
   private var stored: Value
 
   init(initialValue: Value) {
@@ -79,12 +79,12 @@ struct ObservableWrapper<Value> {
 
 // CHECK-LABEL: class_decl{{.*}}"MyObservedType"
 class MyObservedType {
-  @ObservableWrapper var observedProperty = 17
+  @Observable var observedProperty = 17
 
   // CHECK: accessor_decl{{.*}}get_for=observedProperty
-  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.ObservableWrapper.subscript(_enclosingInstance:wrapped:storage:)
+  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:wrapped:storage:)
 
   // CHECK: accessor_decl{{.*}}set_for=observedProperty
-  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.ObservableWrapper.subscript(_enclosingInstance:wrapped:storage:)
+  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:wrapped:storage:)
 }