fix(custom-element): fix that boolean prop with default true can't updated to falsy value

[lejunyang]

close https://github.com/vuejs/core/issues/12214

[github-actions[bot]]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	101 kB (+166 B)	38 kB (+38 B)	34.2 kB (+86 B)
vue.global.prod.js	159 kB (+166 B)	57.9 kB (+43 B)	51.4 kB (-57 B)

Usages

Name	Size	Gzip	Brotli
createApp (CAPI only)	46.9 kB	18.3 kB	16.7 kB
createApp	55 kB	21.3 kB	19.4 kB
createSSRApp	59 kB	23 kB	20.9 kB
defineCustomElement	59.9 kB (+166 B)	22.9 kB (+48 B)	20.8 kB (-26 B)
overall	68.7 kB	26.3 kB	24 kB

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commit: 9cd4dda

[edison1105]

/ecosystem-ci run

[vue-bot]

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[edison1105]

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[yyx990803]

Thanks for the PR! However, the fundamental reason of this bug is _setProp reflecting the attribute change causing mutation observer to be triggered again, which should be avoided in the first place.

I have reused the test from this PR in https://github.com/vuejs/core/commit/352bc88c1bd2fda09c61ab17ea1a5967ffcd7bc0.