Fixed AIOOBE: some property names may not have description.
Code cleanup: redundant overriding removed.
Code cleanup: unused import has been removed
RUBY-13071: (refactoring) hiding RegExpPropertyImpl.PROPERTY_NAMES from RegExpDocumentationProvider.
RUBY-13071: (refactoring) RegExpPropertyImpl.PROPERTY_NAMES made private
RUBY-13071: making RegExpCompletionTest runnable
RUBY-13071: (refactoring) RegExpPropertyNameProvider introduced.
RUBY-13071: (refactoring) RegExpPropertyNameProvider converted from utility class to singleton.
RUBY-13071: (refactoring) more standard name for RegExpPropertyNameProvider's factory method.
RUBY-13071: properties provider is taken from language ext. point
RUBY-13071: (refactoring) better name for default properties provider.
RUBY-13071: (refactoring) RegExpPropertiesProviders.forNode(ASTNode) utility method added to simplify code.