fix: don't set idl on custom elements that are interested in the corresponding content attribute #1643

Job	Run time
Build & Test / Build & Test	1m 34s
Prepare environment	7s
Bench todo / Bench todo/todo	1m 44s
Bench filter-list / Bench filter-list/filter-list	1m 25s
Bench hydrate1k / Bench table-app/hydrate1k	2m 1s
Bench create10k / Bench table-app/create10k	2m 32s
Bench many-updates / Bench many-updates/many-updates	1m 32s
Bench replace1k / Bench table-app/replace1k	2m 59s
Bench text-update / Bench text-update/text-update	59s
Bench 03_update10th1k_x16 / Bench table-app/update10th1k	1m 42s
	16m 35s

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