[Notebook] Create Snapshot directly from any frame in a layout

[charlesh88]

Create snapshot directly from any element's frame in a Display or Flexible Layout.

Design

A new button added to a Layout element's frame that exposes the Snapshot menu.

In the short-term, add the Snapshot button before the current View Large button. In the longer-term, this functionality ties in with the 3 Dots menu design #3298. Right now though, this issue and its UI provides a little more detail on how this button element should work in the short-term. See the UI here: https://drive.google.com/file/d/1QIuOKze72K_SyM1QrH7lMrm_D-1gbNO1/view?usp=sharing

[unlikelyzero]

will retest after #4144

[charlesh88]

Testing Notes

1. Go to a Display Layout, add items to it and save it.
2. Click the camera icon in any object's frame:

3. Choose Save to Notebook Snapshots.
4. Verify that a new Snapshot was created in the Snapshots holder area.
5. Click the thumbnail of the new Snapshot, and verify that the Snapshot image is from that layout frame element:

[charlesh88]

Testathon 8-26-21: verified fixed.

[kobe1104]

Verified fixed - testathon 8/26/2021