longest_match_only default value in Matcher subclasses

[j-rausch]

Describe the bug
When using a simple LambdaFunctionMatcher, I would expect the matcher to return all mentions for which the corresponding function returns True.
However, LambdaFunctionMatcher as a subclass of _NgramMatcher/_Matcher, it has the longest_match_only=True attribute.
This can lead to cases where a sub-span, for witch the lambda function returns True, will not be added as a mention, if its parent span was already matched as True by the matcher.

Expected behavior
Add all spans to the returned mentions, if the lambda function returns True. This could be accomplished by setting longest_match_only to False by default.