Support for ImportQualifiedPost GHC extension

[sonowz]

(This is a feature request)

GHC 8.10.1 introduced a new extension called ImportQualifiedPost.
Basically what it allows is the following syntax:

import A qualified
import B qualified as C

Since the extension is included in the upcoming Haskell standard after Haskell2010, namely GHC2021, I think it would be nice for brittany to have an option to use the new syntax. Any thoughts?

[sonowz]

I think adding a config named like _lconfig_importQualifiedPost :: f (Last Bool) below could work...

brittany/source/library/Language/Haskell/Brittany/Internal/Config/Types.hs

Lines 41 to 56 in 0aa04af

	data CLayoutConfig f = LayoutConfig
	{ _lconfig_cols :: f (Last Int) -- the thing that has default 80.
	, _lconfig_indentPolicy :: f (Last IndentPolicy)
	, _lconfig_indentAmount :: f (Last Int)
	, _lconfig_indentWhereSpecial :: f (Last Bool) -- indent where only 1 sometimes (TODO).
	, _lconfig_indentListSpecial :: f (Last Bool) -- use some special indentation for ","
	-- when creating zero-indentation
	-- multi-line list literals.
	, _lconfig_importColumn :: f (Last Int)
	-- ^ for import statement layouting, column at which to align the
	-- elements to be imported from a module.
	-- It is expected that importAsColumn >= importCol.
	, _lconfig_importAsColumn :: f (Last Int)
	-- ^ for import statement layouting, column at which put the module's
	-- "as" name (which also affects the positioning of the "as" keyword).
	-- It is expected that importAsColumn >= importCol.

I'm feeling like this work needs few changes in the codebase and I can work on it. I'll try 😃