x/website,x/pkgsite: add support for syntax highlighting

[hyangah]

This is an umbrella issue for syntax highlighting support in various web properties owned and maintained by the Go project

• x/pkgsite: code block in comments x/pkgsite: add support for syntax highlighting of code blocks #40952
  example: https://pkg.go.dev/cloud.google.com/go/storage?tab=doc#hdr-Objects
  This can be tricky without a way to distinguish code blocks and pre-formatted non-code blocks.
• x/website: docs and tutorials x/website: Documentation supports code highlighting #55886
  examples:
  - https://go.dev/doc/tutorial/database-access
  - https://go.dev/doc/effective_go
  Source of these pages are html or a simplified md files. https://cs.opensource.google/go/x/website/+/master:_content/doc/
• x/playground, x/pkgsite: x/playground: support for syntax highlighting #34227 x/pkgsite: Syntax Highlight example blocks #52198 x/playground: add code highlighting #28539
  examples:
  - example code https://pkg.go.dev/io#example-Copy
• x/tour: tour partially supports syntax highlighting but that's unmaintained. Recent language updates aren't reflected.
  See x/playground: support for syntax highlighting #34227 (comment) for context.

[danawoodman]

II did a brief experiment to add syntax highlighting via https://github.com/yuin/goldmark-highlighting and it seems fairly easy to accomplish. Is this something the team is open to?

All that I think is required is a bit of configuration of goldmark-highlight and changing a given code block to have the language prefixed with language like you do in Github:

I think it would be pretty easy to progressively add this to pages in an incremental fashion until all properties have syntax highlighting. Is a PR welcome for this?