Set infixr of 'deepseq' to be consistent with 'seq'

[martijnbastiaan]

Without this patch the following code:

a `deepseq` a : as

gets parsed as

(a `deepseq` a) : as

instead of

a `deepseq` (a : as)

Note that seq already behaves like this.

---

We had similar problems over at clash-lang/clash-compiler for our Clash-specific version of deepseq causing pretty bad memory leaks.

[chessai]

So, morally this seems like the right thing to do, but I want to make sure there are no unintended consequences. Can't think of any off the top of my head. CC @haskell/core-libraries-committee

[emilypi]

yeah, this is pretty unoffensive to me.

[chessai]

@martijnbastiaan this needs a changelog entry before merging

[martijnbastiaan]

@chessai Sorry for the delay, done!