drupalBlock() should call hook_block_view_alter()

Problem/Motivation

drupalBlock() builds the block manually but then doesn't call hook_block_view_alter(), thus the block isn't really built identical to how it would be built had this been placed as a block.

Proposed resolution

Add code to \Drupal\twig_tweak\BlockViewBuilder that mimics what happens in \Drupal\Block\BlockViewBuilder.

API changes

Note that an argument was added to the BlockViewBuilder() contructor. To ensure that this is non breaking, I set the new argument's default value of NULL, and retrieve it if it is missing.