enable implied extensions

[shayne-fletcher]

this is an attempt at a fix for #1604. the idea is to make use of extensionImplications

T.hs

import Language.Haskell.TH

oneC, twoC, plusC  :: Quote m => m Exp
oneC = [| 1 |]
twoC = [| 2 |]
plusC = [| $oneC + $twoC |]

main = pure ()

T.hs compiled with cabal run exe:hlint -- -XGHC2021 -XTemplateHaskell ~/RRR.hs fails for lack of HaskellTemplateQuotes before this fix and succeeds after.

[zliu41]

There seems to be some overlap with parts of src/Extension.hs.