improve implicit cradle

[wz1000]

Improve implicit cradles.

Try to match the behaviour of implicit-hie-cradle as closely as possible.

Elminates the need for implicit-hie-cradle and consolidates cradle selection
logic into hie-bios.

1. Prefer cabal over stack (all else being equal)
2. Take work directories into account when making a decision
3. Use implicit-hie to generate stack multi cradles

In particular, this differs from implicit-hie-cradle in that it uses default
(cradle: cabal:) cradles for cabal.

However, we still generate implicit multi-cradles for stack projects by parsing
the stack.yaml and *.cabal files

[wz1000]

I've moved this into HLS proper: haskell/haskell-language-server@178e54f

I change change this to deleting implicit cradle stuff from hie-bios.

[michaelpj]

Let's kill it!

[jhrcek]

@fendor If I understand this correctly, the logic from this PR now lives in hls: https://github.com/haskell/haskell-language-server/blob/master/ghcide/session-loader/Development/IDE/Session/Implicit.hs

So can this PR be closed then?

[fendor]

I think we wanted to remove the implicit cradle logic since we don't need it any more?

[jhrcek]

I can work on that if you give me some pointers, but in any case this PR looks like it's no longer relevant.

[fendor]

To remove the implicit cradle stuff, just start from https://github.com/haskell/hie-bios/pull/422/files#diff-58ae540d147057c94682a01b61de564caf1eb641fac8d2a3f29ea1f29d673ac4L316 and delete stuff until everything's green again :D