[processing] Move destination encoding option to separate menu action

...instead of embedding in output destination file selector. Otherwise
Qt downgrades the file picker to the Qt basic file picker, instead of
the native OS file picker. Which is a huge downgrade and barely
functional for users.

Also remember last selected file format

python/plugins/processing/gui/DestinationSelectionPanel.py

@@ -33,12 +33,13 @@
 from qgis.PyQt.QtCore import QCoreApplication, QDir
 from qgis.PyQt.QtWidgets import QDialog, QMenu, QAction, QFileDialog
 from qgis.PyQt.QtGui import QCursor
-from qgis.gui import QgsEncodingFileDialog, QgsExpressionBuilderDialog
+from qgis.gui import QgsEncodingFileDialog, QgsEncodingSelectionDialog
 from qgis.core import (QgsDataSourceUri,
                        QgsCredentials,
                        QgsExpression,
                        QgsSettings,
                        QgsProcessingParameterFeatureSink,
+                       QgsProcessingParameterRasterDestination,
                        QgsProcessingOutputLayerDefinition,
                        QgsProcessingParameterDefinition,
                        QgsProcessingParameterFileDestination,
@@ -122,6 +123,11 @@ def selectOutput(self):
             actionSaveToFile.triggered.connect(self.selectFile)
             popupMenu.addAction(actionSaveToFile)
 
+            actionSetEncoding = QAction(
+                self.tr('Change file encoding ({})...').format(self.encoding), self.btnSelect)
+            actionSetEncoding.triggered.connect(self.selectEncoding)
+            popupMenu.addAction(actionSetEncoding)
+
             if isinstance(self.parameter, QgsProcessingParameterFeatureSink) \
                     and self.alg.provider().supportsNonFileBasedOutput():
                 actionSaveToSpatialite = QAction(
@@ -208,35 +214,53 @@ def saveToSpatialite(self):
             self.leText.setText("spatialite:" + uri.uri())
 
     def selectFile(self):
-        fileFilter = getFileFilter(self.parameter)
-
+        file_filter = getFileFilter(self.parameter)
         settings = QgsSettings()
+        if isinstance(self.parameter, QgsProcessingParameterFeatureSink):
+            last_ext_path = '/Processing/LastVectorOutputExt'
+            last_ext = settings.value(last_ext_path, '.gpkg')
+        elif isinstance(self.parameter, QgsProcessingParameterRasterDestination):
+            last_ext_path = '/Processing/LastRasterOutputExt'
+            last_ext = settings.value(last_ext_path, '.tif')
+        else:
+            last_ext_path = None
+            last_ext = None
+
+        # get default filter
+        filters = file_filter.split(';;')
+        try:
+            last_filter = [f for f in filters if '*{}'.format(last_ext) in f.lower()][0]
+        except:
+            last_filter = None
+
         if settings.contains('/Processing/LastOutputPath'):
             path = settings.value('/Processing/LastOutputPath')
         else:
             path = ProcessingConfig.getSetting(ProcessingConfig.OUTPUT_FOLDER)
 
-        fileDialog = QgsEncodingFileDialog(
-            self, self.tr('Save file'), path, fileFilter, self.encoding)
-        fileDialog.setFileMode(QFileDialog.AnyFile)
-        fileDialog.setAcceptMode(QFileDialog.AcceptSave)
-        fileDialog.setOption(QFileDialog.DontConfirmOverwrite, False)
-
-        if fileDialog.exec_() == QDialog.Accepted:
+        filename, filter = QFileDialog.getSaveFileName(self, self.tr("Save file"), path,
+                                                       file_filter, last_filter)
+        if filename:
             self.use_temporary = False
-            files = fileDialog.selectedFiles()
-            self.encoding = str(fileDialog.encoding())
-            fileName = str(files[0])
-            selectedFileFilter = str(fileDialog.selectedNameFilter())
-            if not fileName.lower().endswith(
-                    tuple(re.findall("\\*(\\.[a-z]{1,10})", fileFilter))):
-                ext = re.search("\\*(\\.[a-z]{1,10})", selectedFileFilter)
+            if not filename.lower().endswith(
+                    tuple(re.findall("\\*(\\.[a-z]{1,10})", file_filter))):
+                ext = re.search("\\*(\\.[a-z]{1,10})", filter)
                 if ext:
-                    fileName += ext.group(1)
-            self.leText.setText(fileName)
+                    filename += ext.group(1)
+            self.leText.setText(filename)
             settings.setValue('/Processing/LastOutputPath',
-                              os.path.dirname(fileName))
+                              os.path.dirname(filename))
+            if not last_ext_path is None:
+                settings.setValue(last_ext_path, os.path.splitext(filename)[1].lower())
+
+    def selectEncoding(self):
+        dialog = QgsEncodingSelectionDialog(
+            self, self.tr('File encoding'), self.encoding)
+        if dialog.exec_() == QDialog.Accepted:
+            self.encoding = dialog.encoding()
+            settings = QgsSettings()
             settings.setValue('/Processing/encoding', self.encoding)
+        dialog.deleteLater()
 
     def selectDirectory(self):
         lastDir = self.leText.text()

src/gui/qgsencodingfiledialog.cpp

@@ -132,6 +132,7 @@ QgsEncodingSelectionDialog::QgsEncodingSelectionDialog( QWidget *parent, const Q
   layout->addWidget( buttonBox );
   setLayout( layout );
 
+  mEncodingComboBox->addItem( tr( "System" ) );
   mEncodingComboBox->addItems( QgsVectorDataProvider::availableEncodings() );
 
   // Use default encoding if none supplied