Swift SIL: add the Operand.set API

as a shortcut for `Instruction.setOperand`

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/PassManager/Context.swift

@@ -300,11 +300,17 @@ extension AllocRefInstBase {
 extension UseList {
   func replaceAll(with replacement: Value, _ context: some MutatingContext) {
     for use in self {
-      use.instruction.setOperand(at: use.index, to: replacement, context)
+      use.set(to: replacement, context)
     }
   }
 }
 
+extension Operand {
+  func set(to value: Value, _ context: some MutatingContext) {
+    instruction.setOperand(at: index, to: value, context)
+  }
+}
+
 extension Instruction {
   func setOperand(at index : Int, to value: Value, _ context: some MutatingContext) {
     if self is FullApplySite && index == ApplyOperands.calleeOperandIndex {