Improve LifetimeDependence.Scope for mutable trivial variables.

Recognize dependence on the address of a trivial 'var' as an "access" dependence
instead of an "unknown" dependence. This allows the mark_dependence to be
resolved as "[nonescaping]".

SwiftCompilerSources/Sources/Optimizer/Utilities/LifetimeDependenceUtils.swift

@@ -394,6 +394,8 @@ extension LifetimeDependence.Scope {
       self = .borrowed(BeginBorrowValue(bbi)!)
     case is MoveValueInst:
       self = .owned(introducer)
+    case let bai as BeginAccessInst:
+      self = .access(bai)
     default:
       self = .unknown(introducer)
     }