Feature request: update to use webpack builtin output.copy (once webpack 5.111 is out)

**Is your feature request related to a problem? Please describe.**
In looking at Issue #2792 (PR #2794) it was noted that webpack has an upcoming feature to do copy natively rather than requiring a separate plugin.

**Describe the solution you'd like**
Once this feature is in a released version of webpack, refactor to make use of it.

**Describe alternatives you've considered**

Alternative is to continue using the plugin, but this is likely to be deprecated/receive fewer updates once the feature is released in the main package.

**Additional context**
At present this is not in any released version (but is in the main branch). Documentation flags it as available from 5.111.

Wait until webpack 5.111 is released, then inspect the existing copy-plugin configuration and webpack build entry point. Replace the plugin usage with webpack's built-in output.copy support, and confirm that generated assets remain unchanged and the build succeeds.

Written by the indexing model from the issue text.