[GSS](7.2.z) PLINK-792 - Need to set default encoding for FormParserFactory in SPFormAuthenticationMechanism

    public SPFormAuthenticationMechanism(FormParserFactory parserFactory, String name, String loginPage, String errorPage, ServletContext servletContext, PicketLinkType configuration, PicketLinkAuditHelper auditHelper) {
        super(parserFactory, name, loginPage, errorPage);
        this.servletContext = servletContext;
        this.configuration = configuration;
        this.spConfiguration = (SPType) configuration.getIdpOrSP();
        this.auditHelper = auditHelper;
        // we need to create a new formParserFactory to be able to process Multi-Part messages
        this.formParserFactory = FormParserFactory.builder(true).build();                            <- *1
        startPicketLink();
    }

    public static Builder builder(boolean includeDefault) {
        Builder builder = new Builder();
        if (includeDefault) {
            builder.addParsers(new FormEncodedDataDefinition(), new MultiPartParserDefinition());    <- *2
        }
        return builder;
    }

    public static class Builder {

        ...

        public FormParserFactory build() {
            if(defaultCharset != null) {
                for (ParserDefinition parser : parsers) {
                    parser.setDefaultEncoding(defaultCharset);
                }
            }
            return new FormParserFactory(parsers);
        }

    }