Add Eq and Ord instance to `IfaceType`

We add an `Ord` instance so that we can store `IfaceType` in a
`Data.Map` container.
This is required to deduplicate `IfaceType` while writing `.hi` files to
disk. Deduplication has many beneficial consequences to both file size
and memory usage, as the deduplication enables implicit sharing of
values.
See issue #24540 for more motivation.

The `Ord` instance would be unnecessary if we used a `TrieMap` instead
of `Data.Map` for the deduplication process. While in theory this is
clerarly the better option, experiments on the agda code base showed
that a `TrieMap` implementation has worse run-time performance
characteristics.

To the change itself, we mostly derive `Eq` and `Ord`. This requires us
to change occurrences of `FastString` with `LexicalFastString`, since
`FastString` has no `Ord` instance.
We change the definition of `IfLclName` to a newtype of
`LexicalFastString`, to make such changes in the future easier.

Bump haddock submodule for IfLclName changes