Default implementations for redundant PropertyRequiresPlugin methods

[Mechite]

Creates some default implementations returning the opposite of contains and equalTo for their opposing redundant methods.
I don't know why these are here, and perhaps they don't serve a purpose and their usages can be migrated to, well, the opposite of contains and equalTo.

[SentryMan]

LGTM

[rbygrave]

their usages can be migrated to, well, the opposite of contains and equalTo.

Technically this is valid - we could do that.

As I see it, the main reason why we would not do that and stick to missing() and notEqualTo() is because that can be deemed easier to read than the more subtle !.

Example: missing()

    if (builder.contains(Kiwi.class)
      || builder.property().missing("finch-time")
      || builder.property().contains("secondary")) {
      return;
    }

vs !

    if (builder.contains(Kiwi.class)
      || !builder.property().contains("finch-time")
      || builder.property().contains("secondary")) {
      return;
    }

So I think we merge this in - this is definitely an improvement.

There is a followup of if we stop using missing() and notEqualTo() and use ! - is that too subtle / harder to read the generated code etc.