[FLINK-10414][cep] Added skip to next strategy

[dawidwys]

What is the purpose of the change

This pull request adds support of SKIP_TO_NEXT, which will fully cover all variants of AFTER MATCH clause in SQL. This clause is important for e.g. reluctant quantifiers at the end, as after first, shortest match, all others started at the same element will be discarded.

Brief change log

• Added SkipToNextStrategy
• Extended documentation with SKIP_TO_NEXT description

Verifying this change

This change added tests and can be verified as follows:

• org.apache.flink.cep.nfa.AfterMatchSkipITCase#testNoSkipWithQuantifierAtTheEnd
• org.apache.flink.cep.nfa.AfterMatchSkipITCase#testSkipToNextWithQuantifierAtTheEnd
• org.apache.flink.cep.nfa.AfterMatchSkipITCase#testNoSkipWithFollowedByAny
• org.apache.flink.cep.nfa.AfterMatchSkipITCase#testSkipToNextWithFollowedByAny

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[kl0u]

Changes look good.

I would recommend to put the common code of the SkipPastLast with the SkipToNext to a SkipRelativeToPrevMatchStrategy class and have the two strategies above extend that base. This is because the two classes share almost all of their code.

After this, feel free to merge @dawidwys !