Ignore abstract methods when decorating class (#11345)

* Ignore abstract methods when decorating class

* Address Nico's feedback

* Add input/output test

* Update test output to account for _nonIterableRest changes

packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-decorators/ignore-abstract-methods/exec.ts

@@ -0,0 +1,27 @@
+function decorate(value: boolean) {
+  return function(
+    target: any,
+    propertyKey: string,
+    descriptor: PropertyDescriptor
+  ) {};
+}
+
+abstract class A {
+  @decorate(false)
+  private decoratedMember: boolean;
+
+  abstract myMethod(): number;
+}
+
+class B extends A {
+  constructor() {
+    super();
+  }
+
+  myMethod(): number {
+    return 5;
+  }
+}
+
+const b = new B();
+expect(b.myMethod()).toBe(5);

packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-decorators/ignore-abstract-methods/input.ts

@@ -0,0 +1,26 @@
+function decorate(value: boolean) {
+  return function(
+    target: any,
+    propertyKey: string,
+    descriptor: PropertyDescriptor
+  ) {};
+}
+
+abstract class A {
+  @decorate(false)
+  private decoratedMember: boolean;
+
+  abstract myMethod(): void;
+}
+
+class B extends A {
+  constructor() {
+    super();
+  }
+
+  myMethod(): void {
+    
+  }
+}
+
+const b = new B();

packages/babel-helper-create-class-features-plugin/test/fixtures/plugin-proposal-decorators/ignore-abstract-methods/options.json

@@ -0,0 +1,9 @@
+{
+  "presets": [
+    ["typescript"]
+  ],
+  "plugins": [
+    ["proposal-decorators", { "decoratorsBeforeExport": true }],
+    ["proposal-class-properties"]
+  ]
+}