This is only for struct containing nested structs with user defined
mappers.
Add four functions:
1>buildImplicitMap: build map for default mapper
2>buildImplicitMapper: build default mapper.
3>hasUserDefinedMapper for given mapper name and mapper type, lookup
user defined map, if found one return true.
4>isImplicitMapperNeeded check if Mapper is needed
During create map, in checkMappableExpressionList, call
isImplicitMapperNeeded when it return true, call buildImplicitMapper to
generate implicit mapper and added to map clause.
https://github.com/llvm/llvm-project/pull/101101
