Update to webpack 4.47.0

[pjonsson]

What this PR does

Update to webpack 4.47.0

This release supports md4 in Node >=18.

Refs #6998

Test me

The CI tests show the webpack 4.47.0 version being used, but I don't know how to test this beyond that.

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated relevant documentation in doc/.
• I've updated CHANGES.md with what I changed.
• I've provided instructions in the PR description on how to test this PR.

[steve9164]

Thanks Peter. We forgot to check if webpack released a fix on 4.x for this issue, so thanks for doing that and sending in a PR.

Tested against terriajs and TerriaMap build processes, and node 18 & 20.