Improve Screenshots/ViewHierarchy mechanism

[markushi]

Problem Statement

Right now there's little control over capturing Screenshots/VH. This can have a negative impact on the app performance itself (capturing many screenshots, contribution to quota) as well as the usability of the feature itself (no control when a screenshot should be taken or not).

Solution Brainstorm

• Add debouncing mechansim
  Capturing many subsequent screenshots may has a negative performance impact (both CPU and memory).

• Introduce BeforeCaptureScreenshotCalback/BeforeCaptureViewHierarchyCallback
  We want to provide more controls over when and what events for a screenshot should be taken. Thus providing a hook before the screenshot is taken makes most sense here.