OAK-12244: fix cascade delete when node loses mixin indexability

[bhabegger]

OAK-12244: fix mixin type changes not reflected in fulltext index

Root cause: when a node gains or loses a mixin type at runtime,
FulltextIndexEditor did not update the index because propertiesChanged
was never set — jcr:mixinTypes is not normally listed in a rule's
property definitions.

Fix: track wasIndexable (rule matched before) alongside isIndexable()
(rule matches after). In leave(), act on the indexing-rule transition:

• !wasIndexable && isIndexable(): node gained a rule → addOrUpdate
• wasIndexable && !isIndexable(): node lost a rule → deleteDocument

Split FulltextIndexWriter into two explicit operations:

• deleteDocumentTree(path): node physically removed; cascade is correct
• deleteDocument(path): node lost indexability at runtime; exact only

The original deleteDocuments used a PrefixQuery that cascaded to all
descendants; in the mixin-loss branch this was a bug — children carrying
their own mixin types were incorrectly evicted from the index.

Additional changes:

• Snapshot FT_OAK_12244_DISABLE once per commit cycle in FulltextIndexEditorContext
  as typeChangeTrackingEnabled so enter() and leave() always agree
• Skip getApplicableIndexingRule(before) on the hot path via hasNodeTypeChange
  guard when neither jcr:primaryType nor jcr:mixinTypes changed
• Register FT_OAK_12244 toggle in ElasticIndexProviderService
• Reuse CommitFailedException code 5 for the deleteDocument error path

Tests:

• PropertyIndexCommonTest: end-to-end integration tests (all backends)
• LuceneIndexEditor2Test: unit tests verifying writer.docs / writer.deletedPaths
• Verified: 1245 tests, 0 failures in oak-lucene