docs: add docs for v-model update:* event

[xiaodong2008]

Added #2810

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[brc-dd]

Ah, wait this is documented, but it's currently only inside options API block (see later in the document). It should be shown on both composition and options API. It should be similar to what it was earlier - https://github.com/vuejs/docs/blob/7f299d98443efc489115d5f6b64d02094660dbd0/src/guide/components/v-model.md?plain=1 .

[xiaodong2008]

Ah, wait this is documented, but it's currently only inside options API block (see later in the document). It should be shown on both composition and options API. It should be similar to what it was earlier - https://github.com/vuejs/docs/blob/7f299d98443efc489115d5f6b64d02094660dbd0/src/guide/components/v-model.md?plain=1 .

Okay, I will update this.

[xiaodong2008]

Wait, but composition API already have an under the hood part(not complete), and it's not similar to options API, I just completed the part of the parent component, so I think this change is acceptable

https://vuejs.org/guide/components/v-model#under-the-hood