overhaul the token analysis interface

The functional split betweenthe two functions is now that the
first one creates the ID that is used in the word table and
the second one creates the variants. There no longer is a
requirement that the ID is the normalized version. We might
later reintroduce the requirement that a normalized version be available
but it doesn't necessarily need to be through the ID.

The function that creates the ID now gets the full PlaceName. That way
it might take into account attributes that were set by the sanitizers.

Finally rename both functions to something more sane.

nominatim/tokenizer/token_analysis/base.py

@@ -10,22 +10,47 @@ Common data types and protocols for analysers.
 from typing import Mapping, List, Any
 
 from nominatim.typing import Protocol
+from nominatim.data.place_name import PlaceName
 
 class Analyzer(Protocol):
     """ The `create()` function of an analysis module needs to return an
         object that implements the following functions.
     """
 
-    def normalize(self, name: str) -> str:
-        """ Return the normalized form of the name. This is the standard form
-            from which possible variants for the name can be derived.
+    def get_canonical_id(self, name: PlaceName) -> str:
+        """ Return the canonical form of the given name. The canonical ID must
+            be unique (the same ID must always yield the same variants) and
+            must be a form from which the variants can be derived.
+
+            Arguments:
+                name: Extended place name description as prepared by
+                      the sanitizers.
+
+            Returns:
+                ID string with a canonical form of the name. The string may
+                be empty, when the analyzer cannot analyze the name at all,
+                for example because the character set in use does not match.
         """
 
-    def get_variants_ascii(self, norm_name: str) -> List[str]:
-        """ Compute the spelling variants for the given normalized name
-            and transliterate the result.
+    def compute_variants(self, canonical_id: str) -> List[str]:
+        """ Compute the transliterated spelling variants for the given
+            canonical ID.
+
+            Arguments:
+                canonical_id: ID string previously computed with
+                              `get_canonical_id()`.
+
+            Returns:
+                A list of possible spelling variants. All strings must have
+                been transformed with the global normalizer and
+                transliterator ICU rules. Otherwise they cannot be matched
+                against the query later.
+                The list may be empty, when there are no useful
+                spelling variants. This may happen, when an analyzer only
+                produces extra variants to the canonical spelling.
         """
 
+
 class AnalysisModule(Protocol):
     """ Protocol for analysis modules.
     """
@@ -41,7 +66,7 @@ class AnalysisModule(Protocol):
                        as specified in the tokenizer configuration.
                 normalizer: an ICU Transliterator with the compiled normalization
                             rules.
-                transliterator: an ICU tranliterator with the compiled
+                transliterator: an ICU transliterator with the compiled
                                 transliteration rules.
 
             Returns: