[processing] Prefer to log layer source instead of id as it's persistent

(cherry-picked from ba56ba2)

src/core/processing/qgsprocessingparameters.cpp

@@ -3229,7 +3229,13 @@ QString QgsProcessingParameterFeatureSource::valueAsPythonString( const QVariant
     return QgsProcessingUtils::stringToPythonLiteral( layer->source() );
   }
 
-  return QgsProcessingUtils::stringToPythonLiteral( value.toString() );
+  QString layerString = value.toString();
+
+  // prefer to use layer source if possible (since it's persistent)
+  if ( QgsVectorLayer *layer = qobject_cast< QgsVectorLayer * >( QgsProcessingUtils::mapLayerFromString( layerString, context ) ) )
+    layerString = layer->source();
+
+  return QgsProcessingUtils::stringToPythonLiteral( layerString );
 }
 
 QString QgsProcessingParameterFeatureSource::asScriptCode() const

tests/src/analysis/testqgsprocessing.cpp

@@ -4393,6 +4393,7 @@ void TestQgsProcessing::parameterFeatureSource()
   QCOMPARE( def->valueAsPythonString( QStringLiteral( "abc" ), context ), QStringLiteral( "'abc'" ) );
   QCOMPARE( def->valueAsPythonString( QVariant::fromValue( QgsProcessingFeatureSourceDefinition( "abc" ) ), context ), QStringLiteral( "'abc'" ) );
   QCOMPARE( def->valueAsPythonString( QVariant::fromValue( QgsProcessingFeatureSourceDefinition( v2->id() ) ), context ), QStringLiteral( "'%1'" ).arg( vector2 ) );
+  QCOMPARE( def->valueAsPythonString( v2->id(), context ), QStringLiteral( "'%1'" ).arg( vector2 ) );
   QCOMPARE( def->valueAsPythonString( QVariant::fromValue( QgsProcessingFeatureSourceDefinition( QgsProperty::fromValue( "abc" ), true ) ), context ), QStringLiteral( "QgsProcessingFeatureSourceDefinition('abc', True)" ) );
   QCOMPARE( def->valueAsPythonString( QVariant::fromValue( QgsProcessingFeatureSourceDefinition( QgsProperty::fromExpression( "\"abc\" || \"def\"" ) ) ), context ), QStringLiteral( "QgsProperty.fromExpression('\"abc\" || \"def\"')" ) );
   QCOMPARE( def->valueAsPythonString( QVariant::fromValue( QgsProperty::fromExpression( "\"a\"=1" ) ), context ), QStringLiteral( "QgsProperty.fromExpression('\"a\"=1')" ) );