Register obligations during path inference
Fixes#14635
When we infer path expressions that resolve to some generic item, we need to consider their generic bounds. For example, when we resolve a path `Into::into` to `fn into<?0, ?1>` (note that `?0` is the self type of trait ref), we should register an obligation `?0: Into<?1>` or else their relationship would be lost.
Relevant part in rustc is [`add_required_obligations_with_code()`] that's called in [`instantiate_value_path()`].
[`instantiate_value_path()`]: 3462f79e94/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs (L1052)
[`add_required_obligations_with_code()`]: 3462f79e94/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs (L1411)
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