This commit deprecates MediaType.APPLICATION_JSON_UTF8 and
MediaType.APPLICATION_PROBLEM_JSON_UTF8 in favor of
MediaType.APPLICATION_JSON and MediaType.APPLICATION_PROBLEM_JSON since
UTF-8 encoding is now handled correctly by most browsers
(related bug has been fixed in Chrome since September 2017).
MediaType.APPLICATION_JSON is now used as the default JSON content type.
Closes gh-22788
89454e69c3