intl: Return value for IntlDatePatternGenerator::getBestPattern is for IntlDateFormatter (#5567)

* Return value for IntlDatePatternGenerator::getBestPattern is for IntlDateFormatter

Correcting from suggestion it was a format for DateTime.

* Update reference/intl/intldatepatterngenerator/getbestpattern.xml

Co-authored-by: Tim Düsterhus <tim@bastelstu.be>

* Apply suggestions from code review

Had to look this up, but yes it's what is being standardized to.

Co-authored-by: Louis-Arnaud <la.catoire@gmail.com>

* Specify it is a ICU date/time pattern

Applying suggestion @lacatoire #5567 (comment)

---------

Co-authored-by: Tim Düsterhus <tim@bastelstu.be>
Co-authored-by: Louis-Arnaud <la.catoire@gmail.com>

Author: 3 people

reference/intl/intldatepatterngenerator/getbestpattern.xml

@@ -32,9 +32,9 @@
 
  <refsect1 role="returnvalues">
   &reftitle.returnvalues;
-  <para>
-   Returns a format, accepted by <methodname>DateTimeInterface::format</methodname> on success, &return.falseforfailure;.
-  </para>
+  <simpara>
+   Returns an ICU date/time pattern accepted by <classname>IntlDateFormatter</classname> on success, &return.falseforfailure;.
+  </simpara>
  </refsect1>
 
  <refsect1 role="examples">