Rewrite execution model reference

[Josh-Cena]

After 3 years, I finally got around to writing an article on the JavaScript execution model. This page has been a great pain point of mine for a long time. With this update, we:

• Talk about JavaScript, not web API, so less stuff about event loops.
• Introduce post-ES6 formalisms including agents and agent clusters and shared memory.
• Introduce more about function calls and execution contexts.
• Have a much cooler diagram.

This is needed for documentation for advanced features, including memory sharing and shadow realms.

Fix #5006.

[github-actions]

Preview URLs

• /en-US/docs/Web/API/HTML_DOM_API/Microtask_guide
• /en-US/docs/Web/JavaScript/Reference/Execution_model

Flaws (6)

Note! 1 document with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/API/HTML_DOM_API/Microtask_guide
Title: Using microtasks in JavaScript with queueMicrotask()
Flaw count: 6

• broken_links:
  • /en-US/docs/Glossary/user_agent is ill cased
• macros:
  • Macro produces link /en-US/docs/Web/API/Element/select_event which is a redirect
  • Can't resolve /en-US/docs/Web/API/Element/show_event
  • Macro produces link /en-US/docs/Web/API/HTMLElement/input_event which is a redirect
  • Macro produces link /en-US/docs/Web/API/HTMLInputElement/change_event which is a redirect
  • Macro produces link /en-US/docs/Glossary/user_agent which is a redirect

External URLs (3)

URL: /en-US/docs/Web/JavaScript/Reference/Execution_model
Title: JavaScript execution model

• https://html.spec.whatwg.org/multipage/webappapis.html (1 time) (Note! This may be a new URL 👀)
• https://nodejs.org/api/worker_threads.html (1 time) (Note! This may be a new URL 👀)
• https://webkit.org/blog/6240/ecmascript-6-proper-tail-calls-in-webkit/ (1 time) (Note! This may be a new URL 👀)

[OnkarRuikar]

• merge fix(ci): fix URL RXs in linters #38540 and rebase this PR to fix lint check issues.