Add code action for hiding imports

It would be nice if there was a code action for hiding imports which are unused and being shadowed by local declarations.

This is complicated because it requires some detailed information on the provenance of these names in order to hide them (for example if they are record fields).

An example:

Given the following warning:

triangle/Main.hs:83:26: warning: [-Wname-shadowing]
    This binding for ‘window’ shadows the existing bindings
      imported from ‘Graphics.Vulkan’ at triangle/Main.hs:(29,1)-(45,59)
      (and originally defined in ‘Graphics.Vulkan.Extensions.VK_NN_vi_surface’)
      imported from ‘Graphics.Vulkan’ at triangle/Main.hs:(29,1)-(45,59)
      (and originally defined in ‘Graphics.Vulkan.Extensions.VK_KHR_xlib_surface’)
      imported from ‘Graphics.Vulkan’ at triangle/Main.hs:(29,1)-(45,59)
      (and originally defined in ‘Graphics.Vulkan.Extensions.VK_KHR_xcb_surface’)
      imported from ‘Graphics.Vulkan’ at triangle/Main.hs:(29,1)-(45,59)
      (and originally defined in ‘Graphics.Vulkan.Extensions.VK_KHR_android_surface’)

To the hiding list of Graphics.Vulkan add

  XlibSurfaceCreateInfoKHR(window)
, XcbSurfaceCreateInfoKHR(window)
, ViSurfaceCreateInfoNN(window)
, AndroidSurfaceCreateInfoKHR(window)

At the moment this is a pain, as one has to visit each of those modules and find out which record is exposing that name.