codegen: Replace saveIP with InsertPointGuard (#61107)
Replace manual insertion point save/restore operations with RAII-based
InsertPointGuard. This ensures insertion points properly restore debug
information too. With credit to abraemer for diagnosing and suggesting
the fix.
Fix: #61095
Co-authored-by: Adrian Braemer <adrian.braemer@tngtech.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>
(cherry picked from commit 1003b8da6192c47901f1260d47750e7738c34304)
