fix: maintain indexes for REPLACE foreign key actions

[ck89119]

What type of PR is this?

• API-change
• BUG
• Improvement
• Documentation
• Feature
• Test and CI
• Code Refactoring

Which issue(s) this PR fixes:

issue #26875

What this PR does / why we need it:

Fixes REPLACE foreign-key actions when child tables have explicit unique or secondary indexes.

• Keeps binding tags and positional projections only on recursive FK index-maintenance paths.
• Gives hidden-index DELETE operators a stable rowid/primary-key input layout.
• Remaps regular UK/SK pre-insert metadata after projection pruning.
• Preserves secondary-index pre-insert context when copying prepared plans.
• Avoids unsafe optimizer assumptions for untagged internal DML scans.
• Disables the internal RIGHT JOIN runtime filter only when it would create an FK-action wait cycle.
• Adds end-to-end coverage for indexed CASCADE and SET NULL through literal REPLACE and binary-protocol prepared statements.

Validation:

• go test ./pkg/sql/plan
• TestIssue26875ReplaceMaintainsIndexedForeignKeyChildren
• TestIssue25526PreparedUpdateJoinSecondExecute
• golangci-lint run -v -c .golangci.yml ./...