Add TriState toBoolean helper methods

[lynxplay]

While the TriState enum already has helper methods to quickly convert a
boolean into a TriState (both nullable wrappers and their primitive
counterparts), helper methods to convert a TriState back into a boolean
representation are currently missing.

This commit introduces two methods that do exactly that, one
allowing a straight forward conversion to a Boolean as it can represent
a TriState through its nullability as well as another method that
discards the TriState#NOT_SET by accepting a supplier that will be
used to map a not set tri-state.

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I would be very, very happy about suggestions/names for TriState#toBooleanOrElseGet. I based the current method name off of the Optional#orElseGet method that also uses a supplier to map the "not-present" state of an optional, but there might very well be a much better name that I am missing.

[kezz]

Thanks for the PR! Besides the checkstyle issues (which will be flagged up when this build completes), I like this PR! In terms of the implementation, I wonder if we could have the Boolean values as a property of the enum directly.

I'd want to say an Index, but I don't think that supports null values. Maybe a Map<Boolean, TriState> with a map that supports null keys? This could be generated on initialisation using the Boolean values for each enum.

I hope that makes sense :')

[lynxplay]

checkstyle issues (which will be flagged up when this build completes)

were fixed 👍
In regards to the concept of an Index or a Map to map the TriState to a Boolean, a HashMap afaik allows for null as a key. Would you suggest creating a child of the Index utility ?
Tho I am not too sure a map is really needed here. TriState will not outgrow the complexity of two ternary operators anyway concerning the very name of the utility limits it to three states.

[kezz]

Might be worth a toBooleanOrElse method, but it's not massively necessary, and this is just fine regardless :)

[lynxplay]

Might be worth a toBooleanOrElse method, but it's not massively necessary, and this is just fine regardless :)

I'll add it :)

[lynxplay]

Added the toBooleanOrElse method.
Additionally, I expanded the test cases a little, now passing the opposite into the methods that might use a default (e.g. toBooleanOrElse and toBooleanOrElseGet) to ensure that the methods do not accidentally use the default (e.g. true) on a tri-state (e.g. TriState#TRUE).