Support Ruby 3 inline attribute visibility

[theodorton]

See https://redmine.ruby-lang.org/issues/17314

Description

Currently attributes defined with:

private attr_accessor :foo
protected attr_accessor :bar

Will be displayed as public attributes in the documentation.

These should be considered private/protected and not be included in the documentation.

When generating documentation, this warning is show:

[warn]: in YARD::Handlers::Ruby::VisibilityHandler: Undocumentable statement, cannot determine method name
	in file ...:

	1: private attr_accessor :foo

Completed Tasks

• I have read the Contributing Guide.
• The pull request is complete (implemented / written).
• Git commits have been cleaned up (squash WIP / revert commits).
• I wrote tests and ran bundle exec rake locally (if code is attached to PR).