count vs contains (backport from c++20)

alib2abstraction/src/registry/ContainerRegistry.cpp

...experimental/src/grammar/parsing/AbsorbTerminalSymbol.cpp

...o_experimental/src/grammar/parsing/CornerSubstitution.cpp

..._experimental/src/grammar/parsing/ExtractRightContext.cpp

...rimental/src/grammar/parsing/HandleFirstFirstConflict.cpp

...imental/src/grammar/parsing/HandleFirstFollowConflict.cpp

alib2cli/src/command/OverloadsIntrospectionCommand.h

...c/indexes/stringology/SuffixTrieNodeTerminatingSymbol.cpp

...tal/src/indexes/stringology/SuffixTrieTerminatingSymbol.h

...a_experimental/src/string/LinearStringTerminatingSymbol.h

alib2std/src/extensions/container/linear_set.hpp

alib2std/src/extensions/container/map.hpp

alib2std/src/extensions/container/multimap.hpp

alib2std/src/extensions/container/set.hpp

alib2xml/src/registry/XmlContainerParserRegistry.cpp