Codemod v3 slots improvements

[kirillplatonov]

This PR includes improvements for #1669:

• Adds rake task to detect legacy slots bin/rails view_component:detect_legacy_slots
• Adds rake to migrate legacy slots automatically bin/rails view_component:migrate_legacy_slots
• Adds component previews to codemods view paths
• Autodetection for Rails view paths
• Improves uncertain matches detection
• Updated changelog

[kirillplatonov]

@Spone can we merge it at the current state? I included this class in Polaris ViewComponents v1 release and tested upgrade on a couple production apps. It works great.

Even if the current implementation is not perfect it will be beneficial to have it shipped with ViewComponent now when people are doing upgrades to v3. In a couple of months this will be less useful I suppose.

[Spone]

I agree. What do you think @joelhawksley?

[joelhawksley]

I like the idea of getting this into main even if it isn't perfect ❤️

[joelhawksley]

Do you still need this? I'm wary of introducing such a restriction as it is something we'll have to eventually remove.

[kirillplatonov]

Removed it

[kirillplatonov]

@joelhawksley please note that this PR is a contribution to #1669. We'll need to make a final review there once merged.

[Spone]

Let's wrap this up in #1669!