[clang][dataflow] Move logic for `createStorageLocation` from...

[clang][dataflow] Move logic for `createStorageLocation` from `DataflowEnvironment` to `DataflowAnalysisContext`.

`createStorageLocation` in `DataflowEnvironment` is now a trivial wrapper around the logic in `DataflowAnalysisContext`.
Additionally, `getObjectFields` and `getFieldsFromClassHierarchy` (required for the implementation of `createStorageLocation`) are also moved to `DataflowAnalysisContext`.

Reviewed By: gribozavr2, sgatev

Differential Revision: https://reviews.llvm.org/D128359