Add common languages to highlightjs (#953)

* Add common languages to highlightjs

Change the languages highlighted in code blocks:

- Add C and Javascript, which are commonly used with OCaml.

- Add Json, which is used in several major libraries.

- Add SQL and GraphQL, for which popular libraries exist.

- Add Shell Session which seems most useful with Mdx.

The size of highlightjs grows from 33KB to 54KB.

Author: Julow