Remove thread-unsafe context from the AbstractJavadocCheck class 
Now the `AbstractJavadocCheck` class contains some thread-unsafe context, therefore we cannot use the same check instance across multiple threads.

All thread-unsafe members should be rewritten so that they could be used from the separate threads:

1. `parser` - the `JavadocDetailNodeParser` isn't a thread-safe class
1. `blockCommentAst` - the `AbstractJavadocCheck` updates this field in the `visitToken` method