Add resolves this to sinon stub (#29487)

* Add support for resolvesThis() to the SinonStub definition

* Whitespace complaints with lint

types/sinon/index.d.ts

@@ -404,6 +404,10 @@ declare namespace Sinon {
          * If the argument at the provided index is not available, a TypeError will be thrown.
          */
         resolvesArg(index: number): SinonStub;
+        /**
+         * Causes the stub to return a Promise which resolves to its this value.
+         */
+        resolvesThis(): SinonStub;
         /**
          * Causes the stub to throw an exception (Error).
          * @param type

types/sinon/sinon-tests.ts

@@ -404,6 +404,7 @@ function testStub() {
     stub.resolves();
     stub.resolves('foo');
     stub.resolvesArg(1);
+    stub.resolvesThis();
     stub.throws();
     stub.throws('err');
     stub.throws(new Error('err'));