refactor:

- dedupe flash / highlighting logic
- codemirror logic now lives only in codemirror package
- remove old highlighting logic
- use codemirror package in react package
- cleanup CodeMirror6.jsx
- pull setMiniLocations into useHighlighting
- migrate MiniRepl, nano-repl + Repl to new highlighting

packages/codemirror/index.mjs

@@ -0,0 +1,3 @@
+export * from './codemirror.mjs';
+export * from './highlight.mjs';
+export * from './flash.mjs';