Update _redirects for existing v2 runtime warning links

[Jinjiang]

Description of Problem

Some links from v2 runtime warnings currently are broken like:

https://vuejs.org/guide/computed.html (should be https://v2.vuejs.org/v2/guide/computed.html)
https://vuejs.org/guide/list.html#key (should be https://v2.vuejs.org/v2/guide/list.html#Maintaining-State)

Some of them are already redirected to the v3 doc site, which I think inappropriate:

• https://vuejs.org/v2/api/#data -> https://vuejs.org/api/#data no such an anchor and relevant information there
• https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties -> https://vuejs.org/guide/extras/reactivity-in-depth.html no such anchor and relevant information there
• https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function -> https://vuejs.org/guide/essentials/component-basics.html no such anchor and relevant information there

I added 3 new redirects as comments for further discussion.

Proposed Solution

Additional Information

vuejs/vue#12653

Test links:

https://vuejs.org/guide/computed.html
https://v2.vuejs.org/v2/guide/computed.html

https://vuejs.org/guide/custom-directive.html
https://v2.vuejs.org/v2/guide/custom-directive.html

https://vuejs.org/guide/list.html#key
https://v2.vuejs.org/v2/guide/list.html#Maintaining-State

https://vuejs.org/guide/deployment.html
https://v2.vuejs.org/v2/guide/deployment.html

https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties
https://v2.vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties

https://vuejs.org/v2/api/#data
https://v2.vuejs.org/v2/api/#data

https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function
https://v2.vuejs.org/v2/guide/components.html#data-Must-Be-a-Function

[netlify]

✅ Deploy Preview for vuejs ready!

Name	Link
🔨 Latest commit	2831cb7
🔍 Latest deploy log	https://app.netlify.com/sites/vuejs/deploys/62cf28da328b99000aad2e05
😎 Deploy Preview	https://deploy-preview-1832--vuejs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.