improve crate structure & filenames of hackrs_test
Summary:
- move the existing tests into `folded_decl_provider/mod.rs`
- the intent is to provide flexibility allowing for grouping tests by category e.g. `type_provider`, `folded_decl_provider`, ... and sub-categories e.g. `folded_decl_provider::breathing_tests`, `folded_decl_provider::inheritance_tests` and so on
- extend the test context to produce a typing decl provider and also squirrel away the naming provider for completeness
- change the context to hold pointers to trait objects
Differential Revision:
D34763196
fbshipit-source-id:
5d89a3fc5f76be827718d3956369643b5611fcca