Set frame capture timestamp

Unlike SW encoder wrappers, Android HW encoder wrapper uses frame capture timestamp instead of RTP timestamp: https://source.corp.google.com/piper///depot/google3/third_party/webrtc/files/stable/webrtc/sdk/android/src/jni/video_frame.cc;rcl=514125748;l=309

Bug: b/261160916, webrtc:14852
Change-Id: Ief76abae659f7ba890371901cc9b505526ac4f97
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/296500
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39495}

modules/video_coding/codecs/test/video_codec_test.cc

@@ -136,6 +136,7 @@ class TestRawVideoSource : public VideoCodecTester::RawVideoSource {
     auto frame = VideoFrame::Builder()
                      .set_video_frame_buffer(buffer)
                      .set_timestamp_rtp(timestamp_rtp_)
+                     .set_timestamp_us((timestamp_rtp_ / k90kHz).us())
                      .build();
 
     pulled_frames_[timestamp_rtp_] = pulled_frame;