[Fonts] Keep ChatView on the app font and share the report log font

- ChatLog's unset fallback is qApp->font() again: ChatView never set a font
  before the role existed, so an unset role must not switch chat and the game
  log to monospace at the system GeneralFont size.
- Move the monospace fallback the report dialogs used before into
  report_utils::reportLogFont(), which returns the theme's ChatLog role when it
  is set and the old monospace otherwise. tab_report, dlg_my_reports and
  dlg_report_user now share it, so they cannot drift and they honour a themed
  size instead of overriding it.

cockatrice/src/interface/widgets/utility/report_utils.h

@@ -1,6 +1,7 @@
 #ifndef REPORT_UTILS_H
 #define REPORT_UTILS_H
 
+#include <QFont>
 #include <QString>
 #include <QtGlobal>
 
@@ -11,6 +12,12 @@ class ServerInfo_Report;
 namespace report_utils
 {
 
+/** @brief Font for the report chat-log views: the theme's ChatLog role when it
+ *         sets one, otherwise the monospace font these views used before the
+ *         role existed. Shared by the three report surfaces so they cannot
+ *         drift apart. */
+QFont reportLogFont();
+
 QString formatReportCategory(const QString &category);
 QString formatReportTime(qint64 secondsSinceEpoch);