ClangCodeModel: Force clangd restart on external changes

Neither we nor clangd can afford to watch all source files, which means
that after e.g. a branch switch we can easily end up in an inconsistent
state.
We alleviate this problem by restarting clangd if at least one open file
was changed externally.

Change-Id: I7e0d14835e3afbd7a64c3233614f2161282dddc0
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/texteditor/textdocument.h

@@ -120,6 +120,7 @@ public:
     bool isSaveAsAllowed() const override;
     bool reload(QString *errorString, ReloadFlag flag, ChangeType type) override;
     void setFilePath(const Utils::FilePath &newName) override;
+    ReloadBehavior reloadBehavior(ChangeTrigger state, ChangeType type) const override;
 
     QString fallbackSaveAsPath() const override;
     QString fallbackSaveAsFileName() const override;
@@ -155,6 +156,10 @@ public:
     static QAction *createDiffAgainstCurrentFileAction(QObject *parent,
         const std::function<Utils::FilePath()> &filePath);
 
+#ifdef WITH_TESTS
+    void setSilentReload();
+#endif
+
 signals:
     void aboutToOpen(const Utils::FilePath &filePath, const Utils::FilePath &realFilePath);
     void openFinishedSuccessfully();