Git: Add new files with --intent-to-add

Sometimes the file is modified after adding it, either by Qt Creator itself
or by the user.

Running Diff on such a file may look strange. Instead of showing the entire
file, it shows the diff since it was added with its initial content.

Fixes: QTCREATORBUG-23441
Change-Id: I712cc574053f39753250685aec148d2b6d7db192
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/git/gitclient.h

@@ -185,7 +185,8 @@ public:
     bool synchronousLog(const QString &workingDirectory, const QStringList &arguments,
                         QString *output, QString *errorMessage = nullptr,
                         unsigned flags = 0);
-    bool synchronousAdd(const QString &workingDirectory, const QStringList &files);
+    bool synchronousAdd(const QString &workingDirectory, const QStringList &files,
+                        const QStringList &extraOptions = {});
     bool synchronousDelete(const QString &workingDirectory,
                            bool force,
                            const QStringList &files);