MediaTranscodingService: Implement TranscodingRequest.

MediaTranscodingService: Add test assets and more tests for the api.

Bug: 145628554

Test: atest MediaTranscodeManagerTest

Change-Id: Ia77ce381b3bbbe546c96ffe4e1c37675b0d238ee

# Please enter the commit message for your changes. Lines starting

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# Date:      Fri Apr 24 18:05:49 2020 -0700

# Committer: hkuang <hkuang@google.com>

#

# On branch dev9

# Your branch and 'goog/master' have diverged,

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# Changes to be committed:

#	modified:   media/java/android/media/MediaTranscodeManager.java

#	modified:   media/tests/MediaFrameworkTest/Android.bp

#	new file:   media/tests/MediaFrameworkTest/res/raw/VideoOnlyHEVC.mp4

#	modified:   media/tests/MediaFrameworkTest/src/com/android/mediaframeworktest/functional/mediatranscodemanager/MediaTranscodeManagerTest.java

#

# Untracked files:

#	temp

#

        "androidx.test.ext.junit",

        "androidx.test.rules",

        "android-ex-camera2",

        "android-support-test",

        "testng"

    ],

    platform_apis: true,

}