LUCENE-9204: Remove Spans references from DisiWrapper

[romseygeek]

We have a number of helper classes in o.a.l.search that aid the
implementation of two-phase iteration over disjunctions. These have
some Spans-specific code, which will stop compiling once Spans
are moved into the queries module. This commit removes the
Spans references from the main code and duplicates the helper
code within the Spans package.

[romseygeek]

I had hoped to do something similar to what we did for ConjunctionUtils and pull things into shared public factory classes, but that ended up with some very nasty generics code (things like DisiWrapper<T extends DisiWrapper>) so I think just cloning the classes here is unfortunately the correct tradeoff to make.

[mikemccand]

This looks awesome -- it's great to strongly separate spans from disjunctions support classes.

[romseygeek]

Thanks for the reviews @mikemccand!