Inconsistent placement of in depending on the term being annotated

[yannham]

Describe the bug

In a multi-line let-binding, where the in keyword is put on a new line, the indentation of in depends on the presence of a type or a contract annotation on the bound variable, which looks a bit strange and inconsistent.

To Reproduce

Without annotation

let x = 1 + 1
in x

let x = 1 + 1
in
x

let x =
  1 + 1
in x

let x =
  1 + 1
in
x

With an annotation:

let x | Number
  = 1 + 1
  in x

let x | Number
  = 1 + 1
  in
x

let x | Number
  =
    1 + 1
  in x

let x | Number
  =
    1 + 1
  in
x

let x
  | Number
  =
    1 + 1
  in
x

Expected behavior

I see several issues with the current formatting of let-bindings with an annotation. I suppose the general layout idea is to mimic record fields in multiline mode, and to try to put the annotations and the = sign aligned as in the last example. However:

1. Even if the = and the annotation are indented further to be aligned, we should not apply this additional indentation to the in keyword, which should always be indented at the same level as the original let:

   let x
     | Number
     =
       1 + 1
   in
   x
   

2. We should either put both the = and the annotation on their own line, to align them, or let them be and not add any further indentation. The hybrid case, such as:

   let x | Number
     =
       1 + 1
     in
   x
   

   is strange because 1 + 1 seems unduly indented two times, as opposed to the case without an annotation. It should probably be just

   let x | Number =
     1 + 1
   in
   x
   

   as if the annotation was part of the identifier.