Remove (object) casting in block render arrays for configuration

This is dependent upon #1927608: Remove the tight coupling between Block Plugins and Block Entities

Blocks in D7 and were passing a block object through the render array. When the transition to D8 and plugins came around that object was replaced with a simple array of configuration values that represented the block, but this array was cast as an object to ease conversion. The object castings should be removed and the template processing hooks throughout core should be updated appropriately.

Eclipse