Fixes#320507.
The `npmConfigHook` used by `buildNpmPackage` does not correctly
propagate the `nativeBuildInputs` into its `PATH`, which is why `jq` was
not available during the patch phase.
Since this `npmConfigHook` is run as part of a fixed-output
derivation (`fetchNpmDeps`), if it had already been realised, unless its
hash had changed, a missing `jq` would not be noticed, on a rebuild of
`vscode-js-debug`.
The `postPatch` hook is *also* run during `buildNpmPackage`, but there
the `nativeBuildInputs` were correctly added to the `PATH`, which is why
a rebuild of `vscode-js-debug` with the previous `postPatch` would
succeed (if its `npmDeps`'s hash hadn't changed).
