Resolve warning about externalised node dependencies

`npm run build` emits warnings about node dependencies `fs` and `path` which are used by tree-sitter.

```
@getodk/xforms-engine:build: [build:js ] [plugin vite:resolve] Module "fs" has been externalized for browser compatibility, imported by "/home/gareth/src/garethbowen/central-frontend/packages/xpath/dist/expressionParser-i89CXh5o.js". See https://vite.dev/guide/troubleshooting.html#module-externalized-for-browser-compatibility for more details.
```

The correct fix for this is upstream in the web-tree-sitter package: https://github.com/tree-sitter/tree-sitter/issues/5545

Run `npm run build` and review the Vite warning for `fs` and `path` imported by `packages/xpath/dist/expressionParser-i89CXh5o.js`. Read the linked tree-sitter issue to determine whether an upstream fix is available; done means the build no longer emits these externalization warnings.

Written by the indexing model from the issue text.