Add a configuration option to NonLocalExitFromIterator to handle return values.

[sloane]

Fixes #4064.

This solves a long-standing (August 2017) issue. An explicit return in a block has unintuitive behavior where the yield-ing code is skipped.

NonLocalExitFromIterator almost catches this error, it just needs a setting to make it more aggressive.

Example of the type of bug I'm trying to catch:

def execute_with_block
  result = yield
  puts "The result was #{result}"
  result
end

def handle_thing
  execute_with_block do 
    return 3
  end

foo = handle_thing # foo is 3, but the `puts` line never executes

Related: https://github.com/rubocop/rubocop/pull/12971

This is my first PR to Rubocop, so please let me know if I need additional work on this change.

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