Add equals()/hashCode()/toString to IndexType

[romseygeek]

No description provided.

[elasticsearchmachine]

Pinging @elastic/es-storage-engine (Team:StorageEngine)

[romseygeek]

Note that we can't make this a record and keep the private constructor. I'm semi-wondering if I should make this an enum again, but keeping the six boolean fields.

[thecoop]

Its definitely worth a comment on why it shouldn't be a record, to preempt some enthusiastic refactoring. Only certain combinations of IndexType being valid does point towards an enum (which would solve the equals/toString automatically)

[felixbarny]

I still think the way it is right now (not a boolean and not a record) fits this use case well. Especially since there can be a couple of valid permutations for terms and points.

Reading the static factory methods for terms and points again, I noticed they can be simplified by passing in the booleans from the arguments to the constructor directly and return NONE if both arguments are false.