replace linked_hash_map with hashlink

[ghost]

cc contain-rs/linked-hash-map#97

[chyh1990]

it seems that linked-hash-map is quite stable (and used by several popular crates), and we have no reason the switch to a new crate.

[niluxv]

linked-hash-map triggers UB (detected by miri). See the issue you linked and this issue at rustbreak(which has linked-hash-map only as a transitive dependency through this crate and serde_yaml and already triggers UB in the testsuite).

[dessalines]

Since linked_hash_map is broken on rust 1.48.0, and this is affecting downstream projects, this is pressing.

[dessalines]

Any movement on this? This has been preventing projects from using newer rust versions for 2 months now.