Drop stack support for GHC 8.2.2

[fendor]

This is necessary, because when we upgrade cabal-helper,
and transivitely cabal-plan to version 0.5.0.0 in #1126,
the minimum cabal-version is 2.2.
However, each stack snapshot ships with its own version
of cabal-install that can not be changed.

The latest lts for ghc-8.2.2 is 11.18, which ships with
a cabal-install version of 2.0.0.1, which is too old
for cabal-plan 0.5.0.0.

However, in general, there is nothing that forces us to
drop support for GHC 8.2.2. Overriding the compiler version
should be possible, e.g. taking the snapshort 14.8 and
overriding the GHC version, but this requires us
to do manual constraint solving. Could be done if needed.

closes #1425

[alanz]

To me it has been a matter of time before this happens.

[lukel97]

If we’re dropping the snapshot then we might as well drop building with 8.2 entirely, as it won’t get installed in the install script. From what I remember as well there’s a couple of semi group related CPP parts we have for 8.2 which would be nice to drop

[jneira]

I assume that most users could use a ghc version greater than 8.2, but cabal is still able to build with ghc-8.2.2, no? (this is the cabal.project.freeze for cabal freeze -w ghc-8.2.2). stack can't do it due its more reproducible but rigid snapshots.
So build with cabal could be still a workaround for users that have to use it (if we dont remove those cpp's conditions).
Until hie could be used with ghc-8.8 we will support only two main versions of ghc... 🤔

[alanz]

Until hie could be used with ghc-8.8 we will support only two main versions of ghc... thinking

@jneira we will just have to put up with that, people using the older GHC can still use the last hie that supported it.

And I think cabal-plan-0.5.0.0 cannot be built with the older cabal, and won't build with the newer one and GHC 8.2. I remember trying to do that, and coming to the conclusion that we had to drop it.

It has been a second class citizen for some time, running with older versions of things like hlint.

[samuelpilz]

8.2.2 is cited a few times inside the test folder. The cpp call MIN_VERSION_GLASGOW_HASKELL(8,2,2,0) should be upgraded?

[fendor]

One more review, now deletes all legacy code that was necessary for compatibility with GHC 8.2.2. Including tests, dependencies in .cabal files and CI.

[alanz]

Very minor nitpicks of left over comments

[alanz]

LGTM

[samuelpilz]

Files still containing 8.2.2:

test/wrapper/HieWrapper.hs
test/unit/GhcModPluginSpec.hs

[fendor]

HieWrapper tests are simple tests that check that the correct ghc version is discovered, no change necessary.
GhcMod had one unused CPP pragma, which I fixed, and there is a GHC version check in a comment, which I would not like to delete.

[alanz]

I am happy for this to land when CI passes