Add ```language shortcut

[yscik]

Changes proposed in this Pull Request

• Improve the current ``` shortcut to also allow specifying a language

Testing instructions

• Open a post in the block editor
• Type ```php and press enter
• A Syntaxhighlighter Code block should be added with the language set to PHP
• Type ``` and press enter
• The code block should be added with Plain text language

[jom]

Nice feature! I wonder how Gutenberg handles conflicting shortcuts between blocks.

[yscik]

Looks like there is a priority option for transforms, but not sure it applies to this. It's probably working as expected for anyone using this (inserting the Syntaxhighlighter Code block on ```, instead of the core Code block.)