Docs: fix highlighting

[scrhartley]

Description

In PR #1332 the site was moved from Eleventy to Zola. This broke some syntax highlighting, leading to the following build warnings:

Warning: Highlight language shell not found in extensions/preload.md
Warning: Highlight language shell not found in extensions/ws.md
Warning: Highlight language jsx not found in essays/you-cant.md
Warning: Highlight language shell not found in extensions/head-support.md
Warning: Highlight language shell not found in extensions/htmx-1-compat.md
Warning: Highlight language shell not found in extensions/idiomorph.md
Warning: Highlight language shell not found in extensions/response-targets.md
Warning: Highlight language http request not found in essays/why-tend-not-to-use-content-negotiation.md
Warning: Highlight language shell not found in extensions/sse.md
Warning: Highlight language shell not found in docs.md

This PR changes the language aliases to ones that are common to both site builders (see here and here).

Afterwards we are left with:

Warning: Highlight language http request not found in essays/why-tend-not-to-use-content-negotiation.md

I think this was using the http highlight language with Eleventry and there doesn't seem to be an equivalent with Zola.

Corresponding issue: n/a

Testing

Visual inspection with Zola to verify they make a difference and checking errors went away in terminal.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded