Add block alignment support

[yscik]

Code lines are usually longer than text content, and do not work well wrapped, so supporting block alignment options like wide and full width can make life easier.

Changes proposed in this Pull Request

• Move block classes to top-level wrapper element, with wp-block-syntaxhighlighter-code class.
  • This bring the behavior of Additional classes closer to how other blocks work
  • And is needed for some block customization options like alignment and styles
  • Fixes Empty div and no additional class added to code block #146
• Add block alignment support

Testing instructions

• Use a theme with Wide/Full block alignment support, like Twenty Twenty
• Add a Syntaxhighlighter code block, set some block alignment
• Check that it works on the frontend

[jom]

Something with this breaks/does not transform when editing an existing block from master.

[yscik]

Looks like this was just an issue of the base not containing the encoding-related fixes. Rebased onto current master and it's working, even with blocks from 3.5.5.

[jom]

🎉