Add view_component's deprecated slot setters to disallowed_warnings

What does this MR do and why?

Raises an error in development and tests envs when a deprecated slot setter is used with view_component. Example:

- c.body do
  -# ...

This is the last step before we can upgrade to ViewComponent 3.0. I fixed all the deprecation warnings in a series of MRs. Find the checklist and more info in #408988 (closed).

Screenshots or screen recordings

No visual change.

How to set up and validate locally

• As long as CI stays green, we are good here.
• See some of the MRs first CI pipelines for failures.
• To verify locally, pick any usage of a slot setter (- c.with_body do ...), change it back to its old form (- c.body do), run a feature test that renders that partial, see rspec fail locally.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.