Vcs: Introduce IVersionControl::unmanagedFiles()

... and use it in VcsManager::promptToAdd().
This is purely a refactoring. The different IVersionControl subclasses
can (and should) override the naive base class implementation in the
future.

Change-Id: Ifdf49852a98f53a95dad1a89131243b21052bc66
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/coreplugin/iversioncontrol.cpp

@@ -26,6 +26,7 @@
 #include "iversioncontrol.h"
 #include "vcsmanager.h"
 
+#include <utils/algorithm.h>
 #include <utils/hostosinfo.h>
 #include <utils/qtcassert.h>
 
@@ -147,6 +148,14 @@ IVersionControl::~IVersionControl()
     delete m_topicCache;
 }
 
+QStringList IVersionControl::unmanagedFiles(const QString &workingDir,
+                                            const QStringList &filePaths) const
+{
+    return Utils::filtered(filePaths, [wd = QDir(workingDir), this](const QString &f) {
+        return !managesFile(wd.path(), wd.relativeFilePath(f));
+    });
+}
+
 IVersionControl::OpenSupportMode IVersionControl::openSupportMode(const QString &fileName) const
 {
     Q_UNUSED(fileName)