Backport HIE files to GHC 8.6 (#689)

* Backport HIE files support to 8.6

* Use hie files as source of truth for name source spans.

Since we started reusing `.hi` files, this exposes a bug where definitions
aren't available since a bad source span from the `.hi` file gets put into
the NameCache. We rectify by ensuring the span in the NameCache always matches
the one from the `.hie` file.

This has surfaced because an interaction between the commit which uses `.hi`
instead of retypechecking and the change to use the shared global NameCache
to read `.hie` files.

ghcide.cabal

@@ -155,6 +155,14 @@ library
         Development.IDE.Plugin.CodeAction.RuleTypes
         Development.IDE.Plugin.Completions.Logic
         Development.IDE.Plugin.Completions.Types
+    if (impl(ghc > 8.5) && impl(ghc < 8.7)) && !flag(ghc-lib)
+      hs-source-dirs: src-ghc86
+      other-modules:
+        Development.IDE.GHC.HieAst
+        Development.IDE.GHC.HieBin
+        Development.IDE.GHC.HieTypes
+        Development.IDE.GHC.HieDebug
+        Development.IDE.GHC.HieUtils
     if (impl(ghc > 8.7) && impl(ghc < 8.10)) || flag(ghc-lib)
       hs-source-dirs: src-ghc88
       other-modules: