LanguageClient: clear running progress when resetting client

Otherwise we will have dangling progress bars after a crashed server was
restarted.

Change-Id: I889d201d7cf196623978638db67397203a8f4564
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/languageclient/progressmanager.h

@@ -48,6 +48,7 @@ public:
     void handleProgress(const LanguageServerProtocol::ProgressParams &params);
     void setTitleForToken(const LanguageServerProtocol::ProgressToken &token,
                           const QString &message);
+    void reset();
 
     static bool isProgressEndMessage(const LanguageServerProtocol::ProgressParams &params);