Use DeriveLift to generate yesod-core's Lift instances

[RyanGlScott]

GHC 8.0 and later come with the DeriveLift extension for deriving instances of Language.Haskell.TH.Syntax.Lift. yesod-core supports GHC 8.2 and up, so it is able to make use of this. Not only does DeriveLift make for much shorter code, but it also fixes warnings that you get when compiling yesod-core with GHC 8.10 or later:

[20 of 31] Compiling Yesod.Routes.TH.Types ( src/Yesod/Routes/TH/Types.hs, interpreted )

src/Yesod/Routes/TH/Types.hs:34:10: warning: [-Wmissing-methods]
    • No explicit implementation for
        ‘liftTyped’
    • In the instance declaration for ‘Lift (ResourceTree t)’
   |
34 | instance Lift t => Lift (ResourceTree t) where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/Yesod/Routes/TH/Types.hs:49:10: warning: [-Wmissing-methods]
    • No explicit implementation for
        ‘liftTyped’
    • In the instance declaration for ‘Lift (Resource t)’
   |
49 | instance Lift t => Lift (Resource t) where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^

src/Yesod/Routes/TH/Types.hs:59:10: warning: [-Wmissing-methods]
    • No explicit implementation for
        ‘liftTyped’
    • In the instance declaration for ‘Lift (Piece t)’
   |
59 | instance Lift t => Lift (Piece t) where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^

src/Yesod/Routes/TH/Types.hs:78:10: warning: [-Wmissing-methods]
    • No explicit implementation for
        ‘liftTyped’
    • In the instance declaration for ‘Lift (Dispatch t)’
   |
78 | instance Lift t => Lift (Dispatch t) where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^

This is because DeriveLift fills in implementations of liftTyped, a method that was introduced to Lift in template-haskell-2.16.0.0 (bundled with GHC 8.10).

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

[snoyberg]

Can't believe I never knew about that extension. Thanks!