Swift: Add BinaryExpr.getOperator().

Author: geoffw0

swift/ql/lib/codeql/swift/dataflow/internal/DataFlowPrivate.qll

@@ -155,7 +155,7 @@ private module Cached {
     or
     // flow through nil-coalescing operator `??`
     exists(BinaryExpr nco |
-      nco.getStaticTarget().(FreeFunctionDecl).getName() = "??(_:_:)" and
+      nco.getOperator().(FreeFunctionDecl).getName() = "??(_:_:)" and
       nodeTo.asExpr() = nco
     |
       // value argument

swift/ql/lib/codeql/swift/elements/expr/BinaryExpr.qll

@@ -1,11 +1,14 @@
 private import codeql.swift.generated.expr.BinaryExpr
 private import codeql.swift.elements.expr.Expr
+private import codeql.swift.elements.decl.AbstractFunctionDecl
 
 class BinaryExpr extends Generated::BinaryExpr {
   Expr getLeftOperand() { result = this.getArgument(0).getExpr() }
 
   Expr getRightOperand() { result = this.getArgument(1).getExpr() }
 
+  AbstractFunctionDecl getOperator() { result = this.getStaticTarget() }
+
   Expr getAnOperand() { result = [this.getLeftOperand(), this.getRightOperand()] }
 
   override string toString() { result = "... " + this.getFunction().toString() + " ..." }