[12.x] use fenced code blocks

[browner12]

• better syntax highlighting
• easier copy/pasting of code examples
• consistency throughout docs block

@taylorotwell I started on these changes, and then realized none of my recent indentation changes on 11.x were pulled into master yet. Would those changes merge cleanly into this, or create a lot of manual review merge conflicts? Wanted to double check before I added a lot of extra work for you or me. If they won't merge cleanly, I can just wait for 12.x to come out. If it'll be okay, just convert this to a draft, and I'll keep going.

[taylorotwell]

@browner12 merged 11.x -> master just now.

[shaedrich]

• better syntax highlighting
• easier copy/pasting of code examples
• consistency throughout docs block

Since Laravel uses Torchlight, fenced code blocks also allow for a variety of other awesome features, where beneficial:

• Tabs ([11.x] Adds Pest snippets #9291)
• Filenames ([11.x] Use Torchlight code fence filename attribute #9972)
• Highlighting, focusing, or collapsing specific lines or ranges
• Diffs

[shaedrich]

Since Laravel uses Torchlight, fenced code blocks also allow for a variety of other awesome features, where beneficial

This also allows for the opportunity to make code samples more consistent:

• Include or omit <?php
• Include or omit use statements
• Include or omit surrounding context and "setup" "boilerplate"
• Collapse intermediate lines with or without // …, with another sign, or don't collapse at all
• etc.

see laravel/framework#53244

[browner12]

yup. one step at a time here. keeping it simple to make reviews easier.