Generated XML test result files are not outputting UTF-8 encoded characters correctly using --gtest-output:xml

We have a .cpp google test file, with UTF-8 encoded characters in some of our test names, for example:

`TEST(stringReplace, Can_find_matching_characters_differing_case_Àà)`

When this is executed using the `--gtest-output:xml` flag, it is generating an .xml file which is declared as having UTF8 encoding (``), however those UTF8 characters are each being output as single byte ASCII characters.

This is causing issues when attempting to consume these files through an Azure Pipeline, using the [PublishTestResults](https://github.com/microsoft/azure-pipelines-tasks/tree/master/Tasks/PublishTestResultsV2) task.