Refactor to get rid of outdated enhance-visitors dependency

[andreww2012]

Hello!

I noticed that enhance-visitors package of this package:

• Last updated 10 years ago;
• Brings barely maintained & heavy lodash dependency, which recently received a security vulnerability;
• Quite trivial;
• Virtually used by only 2 ESLint plugins.

In this PR, I decided to refactor the code to remove the dependency on it:

• visitIf wrapper calls was replaced with native control flow expressions;
• mergeVisitors implementation was inlined.

Along with that, I've slightly improve the architecture of the rules creator to get rid of the currentTestNode flag.

[andreww2012]

Thank you :)