[lib] Update assets-webpack-plugin to 5.1.2
Summary:
I updated to the latest version in the 5.x major version (5.1.2). I opted not to upgrade further since version 6 only works with Webpack 5
Depends on D6681
Test Plan:
- I checked the breaking changes in the CHANGELOG.md file. I found this which didn't list anything relevant
- Ran yarn prod in both web and landing. Ran the web app and landing page and played around. (This plugin isn't used in dev mode)
Reviewers: atul
Reviewed By: atul
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D6682