Support ATSC license installation

[ Merge of http://go/wvgerrit/163900/ ]

ATSC licenses can be saved by calling
MediaDrm#setPropertyString("storeAtscLicense",<value>)
where <value> is
"<atsc-key-set-ID>:<license-file-data in Base64 format>"

Before storing an ATSC license a session must be opened and the
ATSC mode must be enabled.

Use MediaDrm#setPropertyString("atscMode","enable");

Bug: 176871821
Test: WV Unit/integration/Luci tests
Test: libwvdrmdrmplugin_hal_test
Test: GtsMediaTestCases
Change-Id: Iec2a8b7f87b1122395d06856202278b92316fdfe

libwvdrmengine/mediadrm/include/WVDrmPlugin.h

@@ -456,6 +456,10 @@ class WVDrmPlugin : public ::aidl::android::hardware::drm::BnDrmPlugin,
           in_keyStatusList,
       bool in_hasNewUsableKey);
   void sendSessionLostState(const std::vector<uint8_t>& in_sessionId);
+
+  WvStatus parseAtscLicenseData(const std::string& value,
+                                std::string* key_set_id,
+                                std::string* serialized_license_data);
 };
 
 }  // namespace widevine