TypeScript compatibility (#379)

* Update file extensions and exports for TypeScript compatibility

* docs: fix typo in getting-started.md

* chore: add no-trailing-punctuation rule to VS Code settings

* feat: add @docusaurus/theme-mermaid for mermaid diagram support

* Update import paths for MermaidDiagram component

* remove redudndant check, use effect only runs after the component is mounted

* Update docusaurus.config.ts to fix syntax error

* bring back check because it's not possible to properly cancel a dynamic import

* feat: optimize dynamic import in CodeBlock component

* chore: update VS Code extensions.json with eslint recommendation

* Update docusaurus.config.ts to add GitHub repository link in header

docs/whatis.md

@@ -2,7 +2,7 @@
 title: What is Actix Web
 ---
 
-import { rustVersion } from "@site/vars";
+import vars from "@site/vars";
 
 # Actix Web is part of an Ecosystem of Crates
 
@@ -16,7 +16,7 @@ We call Actix Web a powerful and pragmatic framework. For all intents and purpos
 An application developed with Actix Web will expose an HTTP server contained within a native executable. You can either put this behind another HTTP server like nginx or serve it up as-is. Even in the complete absence of another HTTP server, Actix Web is powerful enough to provide HTTP/1 and HTTP/2 support as well as TLS (HTTPS). This makes it useful for building small services ready for production.
 
 <p>
-Most importantly: Actix Web runs on Rust { rustVersion } or later and it works with stable releases.
+Most importantly: Actix Web runs on Rust { vars.rustVersion } or later and it works with stable releases.
 </p>
 
 <!-- TODO -->