Prior to this commit, the PrintingResultHandler in MockMvc -- typically
invoked via .andDo(print()) -- printed an `application/json` response
body using the default encoding (ISO-8859-1), which resulted in UTF-8
characters being garbled.
Since an `application/json` response is implicitly encoded using UTF-8,
the PrintingResultHandler now infers UTF-8 encoding for such response
bodies.
Closes gh-27926