VCS: Simplify submit editor accept/close flow

* Replace message box with an error on the output pane.
* Separate logic for accept and close.

Change-Id: Ib9fa201a1a67ee195086f7a22bc6678a9642452a
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/perforce/perforceplugin.cpp

@@ -222,7 +222,7 @@ public:
     void getTopLevel(const FilePath &workingDirectory = {}, bool isSync = false);
 
     void updateActions(ActionState) override;
-    bool submitEditorAboutToClose() override;
+    bool activateCommit() override;
     void discardCommit() override { cleanCommitMessageFile(); }
 
     QString commitDisplayName() const final;
@@ -1526,7 +1526,7 @@ bool PerforcePluginPrivate::isCommitEditorOpen() const
     return !m_commitMessageFileName.isEmpty();
 }
 
-bool PerforcePluginPrivate::submitEditorAboutToClose()
+bool PerforcePluginPrivate::activateCommit()
 {
     if (!isCommitEditorOpen())
         return true;