Embeddable Panel is not reactive to Input Updates

[ThomThomson]

Updating the explicit input of an embeddable in a container does not cause the embeddable panel to re-render that embeddable.

This has caused a number of problems recently:

• After editing a lens embeddable by value, upon returning to the dashboard, a new id must be generated and the entire panel must be replaced.
• The dashboard by value example won't respond properly to input updates on its children
• Showing a placeholder when cloning a panel requires that a new id be generated, and that the placeholder is completely deleted after loading is finished.

Fixing this issue may require changes in multiple places, but the system should be able to support:

• The type of a panel changing, while retaining the same embeddable ID. This means changing the factory.
• The savedObjectId changing should trigger the loading of the new saved object.
• In 'by value' cases, changing out the attributes should properly cause a re-render.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)