Format whitespace between top level declarations

Would there be interest in the option automatically add/manage newlines between top level declarations?

If so, what would the params be? Probably the amount of newlines in between.
There might be some rules for `module` and `import` declarations as well.

Example:
```hs
foo :: Int
foo =
1
bar :: Int
bar =
1

baz :: Int
baz =
1
```

Would format like
```hs
foo :: Int
foo =
1

bar :: Int
bar =
1

baz :: Int
baz =
1
```

No files, tests, or entry points are named. Review how the formatter represents top-level Haskell declarations, then define the option parameters and rules for module and import declarations; done means the example receives the requested configurable spacing.

Written by the indexing model from the issue text.