Port to new Q_UNREACHABLE_RETURN()

This is a semantic patch using ClangTidyTransformator to convert
sequences of Q_UNREACHABLE() + return into Q_UNREACHABLE_RETURN(),
newly added to qtbase.

    const std::string unr = "unr", val = "val", ret = "ret";
    auto makeUnreachableReturn = cat("Q_UNREACHABLE_RETURN(",
                                    ifBound(val, cat(node(val)), cat("")),
                                    ")");
    auto ignoringSwitchCases = [](auto stmt) {
        return anyOf(stmt, switchCase(subStmt(stmt)));
    };

    makeRule(stmt(ignoringSwitchCases(stmt(isExpandedFromMacro("Q_UNREACHABLE")).bind(unr)),
                  nextStmt(returnStmt(optionally(hasReturnValue(expr().bind(val)))).bind(ret))),
             {changeTo(node(unr), cat(makeUnreachableReturn,
                                      ";")), // TODO: why is the ; lost w/o this?
              changeTo(node(ret), cat(""))},
             cat("use ", makeUnreachableReturn));

a.k.a qt-use-unreachable-return.

subStmt() and nextStmt() are non-standard matchers.

Change-Id: I3855b2dc8523db1ea860f72ad9818738162495c6
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

src/plugins/platforms/wayland/qwaylandinputcontext.cpp

@@ -288,8 +288,7 @@ bool QWaylandInputContext::filterEvent(const QEvent *event)
     case XKB_COMPOSE_NOTHING:
         return false;
     default:
-        Q_UNREACHABLE();
-        return false;
+        Q_UNREACHABLE_RETURN(false);
     }
 }