GH-4160: Apply the filter-disjunction rewrite only when the disjuncts are mutually exclusive

[faubulous]

GitHub issue resolved #4160

Pull request Description:

TransformFilterDisjunction rewrites filter(e1 || e2, P) into a disjunction that evaluates P once per disjunct, so a solution satisfying k disjuncts is returned k times where the filter returns it once. FILTER(?x = :c || ?x = :c) returns every matching row twice under the default optimizer, and FILTER(?x = :c || ?x != :d) returns rows with ?x = :c twice; disabling optFilterDisjunction restores the correct multiset.

Two changes together restore filter semantics:

• Repeated disjuncts are dropped first — (A || A) is A — so the degenerate duplicate that generated queries really contain (LDBC SPB emits FILTER(?pf = :c || ?pf = :c)) collapses to a single equality that grounds the pattern, rather than being either doubled (before) or left unoptimized (declined).
• The expansion is applied only when the disjuncts are mutually exclusive: every remaining disjunct must test one and the same variable against a constant (= or sameTerm) and the constants must be pairwise known to be different values (NodeValue.notSameValueAs, with an indeterminate comparison treated as possibly equal). That makes the rewrite an exact partition. The motivating case — ?x IN (...) over distinct constants, including mixed IRI/literal lists — keeps its expansion; every other disjunction is now evaluated as the filter it is.

Several existing algebra tests pinned the unsound expansions; their expectation is now that the filter is left alone.

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• Tests are included.
• Documentation change and updates are provided for the Apache Jena website
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx)

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