fix: JSDoc improvments for accessors, etc. (#5567)

* fix: Revert removal of documentation for get/set accessors.
  
  This partially reverts commit 839cb7b,
  "fix: infinite loop when using defineProperties (#5549)"

* docs: Use @name to attach JSDocs to accessors

  Reintroduce documentation for deprecated properties where it was
  removed when converting them to accessors.

* docs: Remove duplicate @package declarations

* fix: Fix eslint and compiler errors/warnings

* fix: Minor JSDoc tweaks to address comments on PR #5567

core/widgetdiv.js

@@ -58,7 +58,6 @@ let themeClassName = '';
 /**
  * The HTML container for popup overlays (e.g. editor widgets).
  * @type {?Element}
- * @alias Blockly.WidgetDiv.DIV
  */
 let DIV;
 
@@ -84,6 +83,14 @@ const testOnly_setDiv = function(newDiv) {
 exports.testOnly_setDiv = testOnly_setDiv;
 
 Object.defineProperties(exports, {
+  /**
+   * The HTML container for popup overlays (e.g. editor widgets).
+   * @name Blockly.WidgetDiv.DIV
+   * @type {?Element}
+   * @deprecated Use Blockly.WidgetDiv.getDiv() and .setDiv().
+   *     (September 2021)
+   * @suppress {checkTypes}
+   */
   DIV: {
     get: function() {
       deprecation.warn(