fix(watch): replace instance unmounted with scope inactive

[yangmingshan]

Ref: #7330 (comment)

This is solution 2, low risk.
Solution 1: #9948

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	89.4 kB (-47 B)	34 kB (-12 B)	30.7 kB (+11 B)
vue.global.prod.js	146 kB (-47 B)	53.3 kB (-14 B)	47.7 kB (+47 B)

Usages

Name	Size	Gzip	Brotli
createApp	49.8 kB (-47 B)	19.5 kB (-20 B)	17.8 kB (-22 B)
createSSRApp	53.1 kB (-47 B)	20.8 kB (-22 B)	19 kB (-24 B)
defineCustomElement	52 kB (-47 B)	20.2 kB (-21 B)	18.5 kB (-30 B)
overall	63.3 kB (-47 B)	24.4 kB (-23 B)	22.2 kB (-66 B)

[pikax]

/ecosystem-ci run

[vue-bot]

📝 Ran ecosystem CI: Open

suite	result	latest scheduled
language-tools	❌ failure	❌ failure
nuxt	✅ success	❌ failure
pinia	✅ success	✅ success
quasar	✅ 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	❌ failure	❌ failure
vuetify	❌ failure	❌ failure
vueuse	❌ failure	❌ failure
vue-simple-compiler	✅ success	✅ success