Add event for webpack plugin customization (#76477)
Add an event for if webpack plugins customized or not. While
investigating adding this I found that when webpack config is added it
does not propagate the event data because the build workers are opted
out of. I've fixed that bug in this PR as it prohibited the new event
from working. I've added a test for both the found bug as well as the
newly added event.
- [x] Add event for webpack plugin customization
- [x] Fix reporting of features when webpack customization is added (bug
found while working on adding the event)
- [x] Add test for reporting features when webpack customization is
added
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