fix(custom-element): reflect prop default value

[edison1105]

close #9006

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	90.8 kB (+70 B)	34.5 kB (+29 B)	31.1 kB (+30 B)
vue.global.prod.js	148 kB (+70 B)	53.8 kB (+33 B)	48.1 kB (+35 B)

Usages

Name	Size	Gzip	Brotli
createApp	50.8 kB (+25 B)	19.9 kB (+15 B)	18.1 kB (+14 B)
createSSRApp	54.2 kB (+25 B)	21.2 kB (+15 B)	19.3 kB (+14 B)
defineCustomElement	53.2 kB (+70 B)	20.6 kB (+26 B)	18.8 kB (+51 B)
overall	64.6 kB (+25 B)	24.9 kB (+16 B)	22.6 kB (+25 B)

[mgibas]

I’m pretty sure if you’ll set an attribute (setProp-> reflect attr) inside of the constructor, real browser will throw an exception :(

[edison1105]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
language-tools	✅ success	✅ success
nuxt	❌ failure	✅ success
pinia	✅ success	✅ success
primevue	✅ success	✅ success
quasar	✅ success	✅ success
radix-vue	✅ success	✅ success
router	✅ success	✅ success
test-utils	✅ success	✅ success
vant	✅ success	✅ success
vite-plugin-vue	✅ success	✅ success
vitepress	✅ success	✅ success
vue-i18n	✅ success	✅ success
vue-macros	✅ success	✅ success
vuetify	❌ failure	❌ failure
vueuse	✅ success	✅ success
vue-simple-compiler	✅ success	✅ success