Call salvageLoadDebugInfo from splitAggregateLoad

Fixes a know issue in which load splitting drops debug info.

After splitting the load, create a new debug_value instruction for the
loaded memory location, inserting a dereference expression if needed.

This fixes debug information for -Onone debugging. Later, after fixing
optimizations, it will also be called at -O, but not on 5.9.

Fixes rdar://104700920 (At -Onone preserve debug info after splitting loads)
Issue: LLDB missing variables in certain case #62241

(cherry picked from commit 5d3793d)

Author: atrick

lib/SILOptimizer/Utils/CanonicalizeInstruction.cpp

@@ -336,6 +336,10 @@ splitAggregateLoad(LoadOperation loadInst, CanonicalizeInstruction &pass) {
     nextII = killInstruction(extract, nextII, pass);
   }
 
+  // Preserve the original load's debug information.
+  if (pass.preserveDebugInfo) {
+    swift::salvageLoadDebugInfo(loadInst);
+  }
   // Remove the now unused borrows.
   for (auto *borrow : borrows)
     nextII = killInstAndIncidentalUses(borrow, nextII, pass);