Webpack build output should be the same for different build configurations

[petemill]

Webpack references from different architectures' output directories (e.g. Release and Release_arm64) creates different output file names. File names are based on a generated hash / ID of all the paths. This can be observed by comparing file names in e.g. gen/brave/components/web-ui-brave_new_tab/.

See tracking issue at #38435 for more details.

Test plan

One symptom of the webpack build having different filenames on intel vs arm is the NTP producing errors when loading some files (e.g. JS chunks) and so far they have been predictable:

1. Open the universal .app on an intel mac
2. Visit NTP
3. Click Customize
4. Switch to "Top Sites"
5. NTP goes blank due to JS error

-or-

1. Open the universal .app on an intel mac
2. In chrome://flags enable "Brave Search on NTP"
3. Restart browser
4. Visit NTP
5. NTP goes blank due to JS error