Add code action for hiding shadowed identifiers from imports

[berberman]

Closes #156

TODO:

• Handle the case where we need perform hiding on multiple import decls simultaneously
• Write tests

[jneira]

Thanks for this nice code action, lgtm

[berberman]

I made changes in deleteFromImport and hideImplicitPreludeSymbol, and used TypeCheck rule in ghcide code action, so I want to ask review from @konn and @pepeiborra.

[konn]

Really neat! And thank you for an aesthetic improvement for trailing comma!

[pepeiborra]

Thanks!