Use var for variables initialized with type casts

[timtebeek]

What's changed?

Added a new recipe with very limited scope in applying var only where initialized by a type cast within methods.

What's your motivation?

This seemed like a simple and safe, non-controversial usage of var that we can then adopt in our tests, which frequently unpack and cast.

Anything in particular you'd like reviewers to focus on?

Any edge cases where this might be unsafe?

Have you considered any alternatives or workarounds?

Could have also tackled static initializer blocks, but that seemed rare to me to have casts there.