transcoding: Add openFileDescriptor to ITranscodingClientCallback.

This is used to open the file when transcoding service really
starts to process the job.

Bug: 145628554
Test: Build

Change-Id: I2d33e349052a1c14f0b3c99017a653666c52fb49
diff --git a/media/libmediatranscoding/tests/TranscodingClientManager_tests.cpp b/media/libmediatranscoding/tests/TranscodingClientManager_tests.cpp
index 0ae8035..db171ce 100644
--- a/media/libmediatranscoding/tests/TranscodingClientManager_tests.cpp
+++ b/media/libmediatranscoding/tests/TranscodingClientManager_tests.cpp
@@ -59,6 +59,11 @@
 
     virtual ~TestClientCallback() { ALOGI("TestClientCallback destroyed"); };
 
+    Status openFileDescriptor(const std::string& /*in_fileUri*/, const std::string& /*in_mode*/,
+                              ::ndk::ScopedFileDescriptor* /*_aidl_return*/) override {
+        return Status::ok();
+    }
+
     Status onTranscodingFinished(int32_t in_jobId,
                                  const TranscodingResultParcel& in_result) override {
         EXPECT_EQ(in_jobId, in_result.jobId);