refactor: remove any type from ts4.4 upgrade regarding

Removes the `any` type used in the previous ts4.4 upgrade PR when
refering to the style property on the element. Creates a new type to
work around the built in `CSSStyleDeclaration` not including
`webkitTapHighlightColor`.

Author: zarend

src/cdk/drag-drop/drag-ref.ts

@@ -33,6 +33,11 @@ import {getMutableClientRect, adjustClientRect} from './client-rect';
 import {ParentPositionTracker} from './parent-position-tracker';
 import {deepCloneNode} from './clone-node';
 
+// CSSStyleDeclaration does not include webkitTapHighlightcolor. Making a type for this to avoid
+// using `any` type.
+type _CSSStyleDeclaration = CSSStyleDeclaration & { webkitTapHighlightColor?: string|null};
+
+
 /** Object that can be used to configure the behavior of DragRef. */
 export interface DragRefConfig {
   /**
@@ -756,7 +761,8 @@ export class DragRef<T = any> {
     this._toggleNativeDragInteractions();
 
     if (this._handles) {
-      (this._rootElement.style as any).webkitTapHighlightColor = this._rootElementTapHighlight;
+      (this._rootElement.style as _CSSStyleDeclaration).webkitTapHighlightColor =
+        this._rootElementTapHighlight;
     }
 
     if (!this._hasStartedDragging) {
@@ -884,7 +890,7 @@ export class DragRef<T = any> {
     // otherwise iOS will still add it, even though all the drag interactions on the handle
     // are disabled.
     if (this._handles.length) {
-      const rootStyles = rootElement.style as any;
+      const rootStyles = rootElement.style as _CSSStyleDeclaration;
       this._rootElementTapHighlight = rootStyles.webkitTapHighlightColor || '';
       rootStyles.webkitTapHighlightColor = 'transparent';
     }