fix: preserve manually-created partial indexes when `partialIndexes` preview feature is disabled (#5790)
Fixes #5789 and https://github.com/prisma/prisma/issues/29289
### Problem
#5780 stripped partial index predicates when `partialIndexes` is
disabled, but manually-created partial indexes were still dropped as
drift.
### Solution
- Track indexes whose predicates were stripped due to feature-gating in
`SqlSchema::feature_gated_partial_indexes`
- Exclude them from `dropped_indexes` in the differ
### Changes
- `sql-schema-describer`: Added `feature_gated_partial_indexes:
HashSet<IndexId>` to track stripped indexes
- `sql-schema-connector`: Skip feature-gated partial indexes in
`dropped_indexes`
- Added regression tests for PostgreSQL, MSSQL, SQLite, and CockroachDB
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **Bug Fixes**
* Manual partial indexes are preserved (not dropped) when the
partialIndexes preview feature is disabled, improving schema sync and
diff stability.
* **New Features**
* Schema describe outputs now include metadata about stripped partial
indexes and an API to query that state.
* Preview-feature flags are propagated through diff and diagnose flows
so tooling respects preview settings.
* **Tests**
* Added cross‑database tests ensuring manual partial indexes are ignored
by migrations/diffs when the preview feature is off.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
prisma-engines
ab73dcf0 - fix: preserve manually-created partial indexes when `partialIndexes` preview feature is disabled (#5790)
