Enable potential_query_instability lint in rustc_hir_typeck.
Fix linting errors by using `FxIndex(Map|Set)` and `Unord(Map|Set)` as appropriate. Part of [MCP 533](https://github.com/rust-lang/compiler-team/issues/533).
I really like the `potential_query_instability` lint!
r? `@lcnr`