Update datatables npm packages to supported versions, remove Assets workaround (OSOE-404)

[0liver]

This is a follow-up issue to OSOE-84.

Problem

Currently, Lombiq.DataTables uses patched versions of datatables.net base on 1.10.25 and datatables.net-bs4 based on 3.2.2.

The patches should long be available in newer releases, and we should return to using regular npm package dependencies to manage them.

Solution

1. Add datatables.net and datatables.net-bs4 back to package.json dependencies.
2. Update all dependencies to stable releases.
3. Remove the Assets/UnmanagedNodeModules folder.
4. Adjust the nodejsExtensions.assetsToCopy config object in package.json to copy the respective files from there instead of UnmanagedNodeModules.
5. Also remove .github\actions\spelling\excludes.txt.

Jira issue