Use exact print to extend import lists

[berberman]

Rework haskell/ghcide#942

Things to do:

• Replace mkVarName and mkTcClsName with parseIdentifier
• Compatible with multiple GHC versions
• Apply changes to CodeAction.hs
• Make tests pass

[berberman]

Parsed source returned by GetAnnotatedParsedSource does not preserve comments, so rewriting may cause stripping of inline comments.

@pepeiborra Can I change the following GetParsedModule to GetParsedModuleWithComments ?

haskell-language-server/ghcide/src/Development/IDE/GHC/ExactPrint.hs

Line 80 in fdb8e5d

pm <- use GetParsedModule nfp

[pepeiborra]

Fantastic work, thank you so much!

[berberman]

Hmm, the test suite of eval plugin failed again and again...

[pepeiborra]

@berberman with this change and a bit more work I think we can restore the work that @gdevanla did to automatically extend imports on completions. Do you or @gdevanla already plan to do it?

[gdevanla]

I have been busy and have not caught up with many things that have happened since last month. I know @pepeiborra had to disable extending imports. I can take a look at it if @berberman has not already done any work on that.

[berberman]

@pepeiborra I'm not familiar with code responsible for completions, and have not investigated yet. So please let @gdevanla do that.

[pepeiborra]

@gdevanla @berberman I was actually planning to look at it today, was just checking that no one else was already working on it.