operation rebase_on logic

[dariuszkuc]

Implements logic to rebase fragments/selections on a given schema.

This is a big PR that introduces some to the underlying selection set data structures - NormalizedFragmentSpreadSelection now includes a selection set from corresponding fragment definition. This now matches how they were represented in both JS and RS implementations.

Some differences between implementations:

• spread selection does not store NamedFragments in RS implementation and instead we just pass those over whenever needed
• NamedFragments are using IndexMap to store NormalizedFragments and is initialized in their dependency order (i.e. if fragment A depends on B then B will be inserted first). Since they are initialized in order, we no longer need to apply the mapInDependencyOrder for other operations -> this method was now renamed to initialize_in_dependency_order
• RebasedFragments now store empty NamedFragments, in JS implementation those values were undefined

[dariuszkuc]

@goto-bus-stop @SimonSapin I addressed all the comments -> please take a look whenever you got a sec