Prior to this commit, MockHttpServletResponse's setCharacterEncoding()
method did not update the contentType property, which violates the
Servlet 2.4 Javadoc for getContentType() and setCharacterEncoding().
This commit addresses this issue; however, some existing tests may have
to be updated as a result of this change.
For example, note how some of the tests in this commit have been
refactored to use MediaType##isCompatibleWith() instead of asserting
exact matches for the value returned by MockHttpServletResponse's
getContentType() method.
Closes gh-25536
Prior to this commit, calling reset() on MockHttpServletResponse did not
reset the `charset` field to `false` which could result in the
"Content-Type" header containing `;charset=null` which in turn would
result in errors when parsing the "Content-Type" header.
This commit resets the charset field to `false` in
MockHttpServletResponse's reset() method to avoid such errors.
Closes gh-25501
Prior to this commit, if the user supplied a comma-separated list such
as "en, it" as the Content-Language header value to
MockHttpServletResponse's setHeader() method, only the first language
was actually set in the response's Content-Language header (e.g., "en").
This commit ensures that all supplied content languages are set in the
response's Content-Language header.
Closes gh-25281
Rossen Stoyanchev