OAK-12348: Property and node type indexes support costPerEntry/costPerExecution overrides

[bhabegger]

What

PropertyIndex/NodeTypeIndex (oak-core) compute query cost purely from
indexed entry counts plus a fixed overhead of 2, with no way to influence
the estimate from the index definition — unlike Lucene/Elastic indexes
(oak-search), which already read costPerEntry/costPerExecution.

In production this let the nodeType/property index win a cost comparison
against a more selective, purpose-built index for the same query, because
the built-in entry-count estimate can be significantly wrong at scale (seen
in three related incidents on rep:User/rep:Group queries against a
tagged authorizables Lucene index). The workaround each time was a
manual costPerEntry/costPerExecution override — but that only exists on
the Lucene/Elastic side.

How

PropertyIndexPlan and PropertyIndexLookup each split into:

• getCostLegacy(...) — the original hardcoded formula, unconditionally.
• getCostConfigurable(...) — cost = costPerExecution + costPerEntry * entryCount,
  both optionally set on the property index definition (new IndexConstants.COST_PER_ENTRY/
  COST_PER_EXECUTION, same property names oak-search's FulltextIndexConstants
  already uses for Lucene/Elastic).
• getCost(...) — dispatches between the two based on FT_OAK-12348
  (PropertyIndexLookup.FT_OAK_12348_ENABLE), enabled by default: with
  no properties set, getCostConfigurable() reproduces getCostLegacy()
  exactly, so this is behavior-preserving for every existing index
  definition — the toggle is an escape hatch, not an opt-in gate.

NodeTypeIndex needs no code changes at all — its cost is the sum of two
PropertyIndexLookup.getCost() calls (jcr:primaryType, jcr:mixinTypes),
so it picks up the override transitively (covered by a dedicated test).

IndexUtils gains a small getOptionalValue(NodeState, String, double)
helper (mirrors oak-search's IndexDefinition.getOptionalValue, which
oak-core can't depend on directly) instead of duplicating the same
property read in both classes.

Out of scope: resultCacheSize (mentioned in the originating request) is a
Lucene/Elastic query-result caching concept with no equivalent in
PropertyIndex's ContentMirrorStoreStrategy-based lookup.

Testing

New/updated tests in PropertyIndexTest, PropertyIndexLookupTest (unchanged,
still green), and NodeTypeIndexTest cover: default behavior unchanged
regardless of toggle position, override taking effect by default, the
toggle correctly falling back to the legacy formula when disabled, the
costPerEntry=0 infinity-guard (must not become NaN), the unique-index
short-circuit surviving an override, and NodeTypeIndex picking up the
override with zero code changes in its own package.

Full oak-core suite: 4779 tests, 0 failures.