Use type aliases FilePath, FilePaths...

... for wxString and wxArrayStringEx, holding file paths (absolute or relative,
directory or plain file); to be replaced later with different types

(not yet using std::vector, becase of some uses of wxArrayString::Index with
two arguments)

src/export/Export.cpp

@@ -616,7 +616,7 @@ bool Exporter::GetFilename()
          }
       }
 
-      const auto &ext = mFilename.GetExt();
+      auto ext = mFilename.GetExt();
       defext = mPlugins[mFormat]->GetExtension(mSubFormat).Lower();
 
       //

src/export/ExportMultiple.cpp

@@ -638,7 +638,7 @@ ProgressResult ExportMultiple::ExportMultipleByLabel(bool byName,
    // Figure out how many channels we should export.
    auto channels = mTracks->GetNumExportChannels(false);
 
-   wxArrayString otherNames;  // keep track of file names we will use, so we
+   FilePaths otherNames;  // keep track of file names we will use, so we
    // don't duplicate them
    ExportKit setting;   // the current batch of settings
    setting.destfile.SetPath(mDir->GetValue());
@@ -754,7 +754,7 @@ ProgressResult ExportMultiple::ExportMultipleByTrack(bool byName,
    bool tagsPrompt = mProject->GetShowId3Dialog();
    int l = 0;     // track counter
    auto ok = ProgressResult::Success;
-   wxArrayString otherNames;
+   FilePaths otherNames;
    std::vector<ExportKit> exportSettings; // dynamic array we will use to store the
                                   // settings needed to do the exports with in
    exportSettings.reserve(mNumWaveTracks);   // Allocate some guessed space to use.

src/export/ExportMultiple.h

@@ -127,7 +127,7 @@ private:
    bool mInitialized;
 
    // List of file actually exported
-   wxArrayString mExported;
+   FilePaths mExported;
 
    wxChoice      *mFormat;    /**< Drop-down list of export formats
                                 (combinations of plug-in and subformat) */