deal with unwanted side-effects of gap-system#3006

- Let the filters created by `DeclareHandlingByNiceBasis` imply
  `IsFreeLeftModule`.
  This was the case before the changes from gap-system#3006, and this change fixes
  the problem described in gap-system#5322, as I had sketched in the discussion of gap-system#5325.
- Document this change (following gap-system#5325).
- Increase the rank of `IsHandledByNiceBasis` by 2.
  Then we get back to the rank before the changes from gap-system#3006.
  This way, the `\in` method with second argument in
  `IsFreeLeftModule and IsHandledByNiceBasis` is again ranked higher than
  the one with second argument `IsFreeLeftModule and IsFiniteDimensional`.
  The bug described in issue gap-system#5334 which has been found because of the
  reordering of these two methods (due to gap-system#3006)
  gets fixed via pull request gap-system#5335,
  now we can return to the better method ordering.
  (I do not like uprankings, but I have no better idea to solve this problem.)

lib/basis.gd

@@ -786,9 +786,10 @@ DeclareOperation( "RelativeBasisNC", [ IsBasis, IsHomogeneousList ] );
 ##  (see&nbsp;<Ref Sect="Vector Spaces Handled By Nice Bases"/>).
 ##  <P/>
 ##  <A>name</A> must be a string,
-##  a filter <M>f</M> with this name is created, and
+##  a filter <M>f</M> with this name is created which implies
+##  <Ref Filt="IsFreeLeftModule"/>, and
 ##  a logical implication from the join of <M>f</M> with
-##  <Ref Filt="IsFreeLeftModule"/> and <Ref Filt="IsAttributeStoringRep"/> to
+##  <Ref Filt="IsAttributeStoringRep"/> to
 ##  <Ref Filt="IsHandledByNiceBasis"/> is installed.
 ##  <P/>
 ##  <A>record</A> must be a record with the following components.
@@ -895,6 +896,7 @@ DeclareGlobalFunction( "CheckForHandlingByNiceBasis" );
 InstallGlobalFunction( "DeclareHandlingByNiceBasis", function( name, info )
     local entry;
     DeclareFilter( name );
+    InstallTrueMethod( IsFreeLeftModule, ValueGlobal( name ) );
     entry := [ ValueGlobal( name ), info ];
     Add( NiceBasisFiltersInfo, entry, 1 );
 end );

lib/basis.gi

@@ -693,7 +693,7 @@ InstallGlobalFunction( "InstallHandlingByNiceBasis",
     entry:= First( NiceBasisFiltersInfo,
                    x -> IsIdenticalObj( filter, x[1] ) );
     entry[3] := record.detect;
-    filter:= filter and IsFreeLeftModule and IsAttributeStoringRep;
+    filter:= filter and IsAttributeStoringRep;
     InstallTrueMethod( IsHandledByNiceBasis, filter );
 
     # Install the methods.

lib/module.gd

@@ -247,8 +247,10 @@ DeclareProperty( "IsFullMatrixModule", IsFreeLeftModule, 20 );
 ##  </ManSection>
 ##  <#/GAPDoc>
 ##
-DeclareCategory( "IsHandledByNiceBasis", IsFreeLeftModule );
-#T why not `DeclareFilter' ?
+DeclareCategory( "IsHandledByNiceBasis", IsFreeLeftModule, 3 );
+# We want that 'IsFreeLeftModule and IsHandledByNiceBasis' has a higher rank
+# than 'IsFreeLeftModule and IsFiniteDimensional'.
+# (There are concurrent '\in' methods for the two situations.)
 
 
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