Add @query_plan_xml parameter to sp_QueryReproBuilder

New parameter lets callers feed a single query plan XML directly, bypassing
Query Store entirely. Useful for isolating plans that are slow to parse and
iterating on them without repeatedly hitting Query Store.

When @query_plan_xml is supplied:
- Database existence check is skipped
- Query Store existence check is skipped
- The entire Query Store population region is skipped (wrapped in
  IF @query_plan_xml IS NULL)
- One synthetic row is seeded into each of #query_store_plan,
  #query_store_query, #query_store_query_text, #query_store_runtime_stats,
  and #query_context_settings with plan_id/query_id = -1 so synthetic rows
  cannot collide with real Query Store data
- Statement text is extracted from the plan's StmtSimple/@StatementText
  to feed #query_store_query_text
- The existing parameter extraction, warnings, embedded-constants, and
  repro-build phases all run unmodified against the synthetic data

USE-database scaffold in the generated repro is gated on @database_name
being supplied so synthetic-mode output doesn't emit 'USE NULL;'.

Tested end-to-end against a parameterized HammerDB plan: @query_plan_xml
round-trips through the parser and produces the parameter name/type/value
plus the full repro scaffold.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: erikdarlingdata