maps "toggleevent-source" web feature

[ChrisC]

web feature docs: https://github.com/web-platform-dx/web-features/blob/main/features/toggleevent-source.yml

@foolip I opted to update the mappings in the the-dialog-element to avoid overlap with the "dialog" web feature in 8940582. You signaled that we should eventually do this when we encountered similar overlap situations on the button element recently. If we should keep dialog as is though, I can revert the commit.

cc @jcscottiii @jugglinmike

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[foolip]

@foolip I opted to update the mappings in the the-dialog-element to avoid overlap with the "dialog" web feature in 8940582. You signaled that we should eventually do this when we encountered similar overlap situations on the button element recently. If we should keep dialog as is though, I can revert the commit.

I think it's the right call. I know we have a lot of features with "subfeatures" that overlap, but in general I think avoiding the overlap is better.