Set `output_encoding` in `FreeMarkerView` implementations

[sbrannen]

Overview

While researching #33071, I discovered that Spring's FreeMarkerView implementations should be configuring the output_encoding for template rendering.

Specifically, The charset for output section of the FreeMarker documentation states the following (bold emphasis added by me).

In principle FreeMarker does not deal with the charset of the output, since it writes the output to a java.io.Writer. Since the Writer is made by the software that encapsulates FreeMarker (such as a Web application framework), the output charset is controlled by the encapsulating software. Still, FreeMarker has a setting called output_encoding (starting from FreeMarker version 2.3.1). The enclosing software should set this setting (to the charset that the Writer uses), to inform FreeMarker what charset is used for the output (otherwise FreeMarker can't find it out). Some features, such as the url built-in, and the output_encoding special variable utilize this information. Thus, if the enclosing software doesn't set this setting then FreeMarker features that need to know the output charset can't be used.

Related Issues

• Improve documentation regarding encoding in FreeMarker support #33071