[afs] Correctly advertise SelectAtId capability

Big speedup for attribute table loading with provider

Author: nyalldawson

src/providers/arcgisrest/qgsafsprovider.cpp

@@ -200,6 +200,11 @@ QgsFields QgsAfsProvider::fields() const
   return mSharedData->mFields;
 }
 
+QgsVectorDataProvider::Capabilities QgsAfsProvider::capabilities() const
+{
+  return QgsVectorDataProvider::SelectAtId;
+}
+
 void QgsAfsProvider::setDataSourceUri( const QString &uri )
 {
   mSharedData->mDataSource = QgsDataSourceUri( uri );

src/providers/arcgisrest/qgsafsprovider.h

@@ -52,7 +52,7 @@ class QgsAfsProvider : public QgsVectorDataProvider
     bool changeAttributeValues( const QgsChangedAttributesMap &attr_map ) override{ return false; }
     bool changeGeometryValues( QgsGeometryMap & geometry_map ) override{ return false; }
     */
-    QgsVectorDataProvider::Capabilities capabilities() const override { return QgsVectorDataProvider::NoCapabilities; }
+    QgsVectorDataProvider::Capabilities capabilities() const override;
     QgsAttributeList pkAttributeIndexes() const override { return QgsAttributeList() << mObjectIdFieldIdx; }
     QgsAttrPalIndexNameHash palAttributeIndexNames() const override { return QgsAttrPalIndexNameHash(); }