feat(core): new APIs for Aspects and Tags (#9558)

In [CDK 2.0], the `applyAspect` API will be removed and instead will be accessible through a "trait" pattern:

    Aspects.of(scope).add(aspect)

Similarly, we are normalizing the tagging API to use the same pattern:

    Tags.of(scope).add(x, y)
    Tags.of(scope).remove(x)
    
The existing APIs are still supported but marked as @deprecated.

Related: aws/aws-cdk-rfcs#192, See [Design].

[CDK 2.0]: https://github.com/aws/aws-cdk-rfcs/blob/master/text/0192-remove-constructs-compat.md
[Design]: https://github.com/aws/aws-cdk-rfcs/blob/master/text/0192-remove-constructs-compat.md#02-aspects

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/core/lib/aspect.ts

@@ -1,5 +1,7 @@
 import { IConstruct } from 'constructs';
 
+const ASPECTS_SYMBOL = Symbol('cdk-aspects');
+
 /**
  * Represents an Aspect
  */
@@ -10,8 +12,6 @@ export interface IAspect {
   visit(node: IConstruct): void;
 }
 
-const ASPECTS_SYMBOL = Symbol('cdk-aspects');
-
 /**
  * Aspects can be applied to CDK tree scopes and can operate on the tree before
  * synthesis.
@@ -25,8 +25,10 @@ export class Aspects {
   public static of(scope: IConstruct): Aspects {
     let aspects = (scope as any)[ASPECTS_SYMBOL];
     if (!aspects) {
-      aspects = Object.defineProperty(scope, ASPECTS_SYMBOL, {
-        value: new Aspects(scope),
+      aspects = new Aspects(scope);
+
+      Object.defineProperty(scope, ASPECTS_SYMBOL, {
+        value: aspects,
         configurable: false,
         enumerable: false,
       });
@@ -36,13 +38,13 @@ export class Aspects {
 
   private readonly _aspects = new Array<IAspect>();
 
-  private constructor(_construct: IConstruct) { }
+  private constructor(private readonly scope: IConstruct) { }
 
   /**
-   * Apply an aspect on this scope.
-   * @param aspect The aspect to apply.
+   * Adds an aspect to apply this scope before synthesis.
+   * @param aspect The aspect to add.
    */
-  public apply(aspect: IAspect) {
+  public add(aspect: IAspect) {
     this._aspects.push(aspect);
   }
 
@@ -52,4 +54,4 @@ export class Aspects {
   public get aspects(): IAspect[] {
     return  [ ...this._aspects ];
   }
-}
+}