GH-0000 Add exhaustive LMDB index selection combinatorics test

[hmottestad]

Summary

• add a focused LMDB test for TripleStore#getBestIndex
• generate all 24 index permutations and all non-empty configured-index combinations up to 6 indexes
• verify all 16 statement-pattern bind/wildcard combinations select a best-scoring index

Verification

• mvn -o -Dmaven.repo.local=.m2_repo -pl core/sail/lmdb -Dformatter.skip=true -Dimpsort.skip=true -Dtest=TripleStoreIndexSelectionCombinatoricsTest verify