workaround API build failing on 5 files:

- these files used {string}, which is now evaluated as an expression in mdx (https://mdxjs.com/docs/what-is-mdx/#expressions)
-> setup docusaurus to only use mdx on .mdx files, because api is generated as normal .md

The docusaurus CommonMark feature is experimental: https://docusaurus.io/docs/markdown-features#mdx-vs-commonmark
With following limitations:facebook/docusaurus#9092

For reference, failing files were:
- "/api/Dalamud.Interface.Utility/Structs/ImVectorWrapper`T`"
- "/api/Dalamud.Utility.Timing/Classes/Timings"
- "/api/Dalamud.Utility/Classes/DisposeSafety.ScopedFinalizer"
- "/api/FFXIVClientStructs.Interop/"
- "/api/FFXIVClientStructs.Interop/Structs/SpanExtensions.SpanPointerEnumerator`T`"

docusaurus.config.js

@@ -24,6 +24,12 @@ const config = {
   onBrokenLinks: 'ignore',
   onBrokenMarkdownLinks: 'warn',
 
+  // Some API comments contain curly brackets \{expression\} which are in the new mdx evaluated as expressions
+  // 'detect' uses mdx for .mdx files and CommonMark
+  markdown: {
+    format: 'detect',
+  },
+
   webpack: {
     jsLoader: (isServer) => ({
       loader: require.resolve('swc-loader'),