generalize normalization step for search query

It is now possible to configure functions for changing the query
input before it is analysed by the tokenizer.

Code is a cleaned-up version of the implementation by @miku.

src/nominatim_api/query_preprocessing/base.py

@@ -0,0 +1,32 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# This file is part of Nominatim. (https://nominatim.org)
+#
+# Copyright (C) 2024 by the Nominatim developer community.
+# For a full list of authors see the git log.
+"""
+Common data types and protocols for preprocessing.
+"""
+from typing import List, Callable
+
+from ..typing import Protocol
+from ..search import query as qmod
+from .config import QueryConfig
+
+QueryProcessingFunc = Callable[[List[qmod.Phrase]], List[qmod.Phrase]]
+
+
+class QueryHandler(Protocol):
+    """ Protocol for query modules.
+    """
+    def create(self, config: QueryConfig) -> QueryProcessingFunc:
+        """
+        Create a function for sanitizing a place.
+        Arguments:
+            config: A dictionary with the additional configuration options
+                    specified in the tokenizer configuration
+            normalizer: A instance to transliterate text
+        Return:
+            The result is a list modified by the preprocessor.
+        """
+        pass