[Feature Request]: Add a rule against unused imports

[strangerkir]

Is your feature request related to a problem?

After code refactoring or merging, we often have redundant namespace imports with the use keyword. This is a dead code that does nothing but pollution. It's easy to overlook these lines.

Describe the desired solution

Add a sniff raising warning or error on redundant namespace imports.

Describe the alternatives that you have considered

Require the code standard with this rule and just use it.

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[gmazzap]

We have added Slevomat standard as a dependency.

Thar standard has a lot of Sniffs, so we could use much more sniff besides the "unused use" proposed here.
But we need to gather consensus on the sniffs to require.

[gmazzap]

Closing in favor of #71