TH: handle explicit quantification in instanceswip/instd-quantifications

This patch adds support for explicitly-written quantification in
typeclass instances, such as:

  instance forall k (a :: k). C a
  deriving instance forall k (a :: k). D a

It does so by adding a field of type `Maybe (TyVarBndr ())`
to both the `InstanceD` and `StandaloneDerivD` constructors of the
Template Haskell `Dec` datatype, and making appropriate use of it to
ensure that spliced declarations don't silently drop the user-written
quantification.

Fixes #21794

Updates haddock submodule

1 files changed, 0 insertions, 0 deletions

diff --git a/utils/haddock b/utils/haddock
-Subproject 519a95998b09a2c9c7a42c3a0cf2ca0c4358bb4
+Subproject b50bc29c190ca0f6ca35a6fcbd1657b0d28753c