Markdown syntax migration script

Script replacing include_code with code-snippet

Migration script: partials, some variables

Add variables to conversion script

draft repo-link component

Complete repo-link component

Migration script: handle github links

Draft include_svg→inline-svg (non-functional)

Currently doesn't work due to image path issues.
Also, captions and custom classes (for inlining) not implemented yet.

Conversion script: refactor & add code-page-name

Custom code-page-name component works around Markdoc limitation where
vars can't be used in `inline code` sections.

Migrate script: Handle more code includes correctly

Migration script: tabs and tabbed code samples

Child pages macro & conversion script

Adapted from 70cffa67ed

Migration script: update with some partial fixes

Migration script: callouts→admonitions

Fix auto-generation of index pages

Migration script: fix SVG migration

Migration scripting: fix code block prefixes & indentation

- Use the Redocly 0.66 feature for code block prefixes
- Update the script for converting indented code blocks to fences with
  Roman's latest fixes (now uses 4 spaces per level, for consistency)

package.json

@@ -10,7 +10,7 @@
   "keywords": [],
   "license": "MIT",
   "dependencies": {
-    "@redocly/portal": "0.57.0",
+    "@redocly/portal": "^0.65.3",
     "lottie-react": "^2.4.0",
     "moment": "^2.29.4"
   },