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/cdm/core/src/device_files.cpp

@@ -943,6 +943,11 @@ bool DeviceFiles::RetrieveLicense(const std::string& key_set_id,
                                       &license_data->wrapped_private_key);
 }
 
+DeviceFiles::ResponseType DeviceFiles::StoreAtscLicense(
+    const CdmKeySetId& key_set_id, const std::string& serialized_data) {
+  return StoreFileWithHash(key_set_id + kLicenseFileNameExt, serialized_data);
+}
+
 bool DeviceFiles::DeleteLicense(const std::string& key_set_id) {
   RETURN_FALSE_IF_UNINITIALIZED();
   return RemoveFile(key_set_id + kLicenseFileNameExt);