SI-9008 Fix regression with higher kinded existentials

Allow a naked type constructor in an existential type if
we are directly within a type application.

Recently, 84d4671 changed nested context creation to avoid passing
down the `TypeConstructorAllowed`, which led to missing kind errors
in code like `type T[({type M = List})#M]`.

However, when typechecking `T forSome { quantifiers }`, we create
a nested context to represent the nested scope introduced for the
quantifiers. But we need to propagate the `TypeConstructorAllowed`
bit to the nested context to allow for higher kinded existentials.

The enclosed tests show:
  - pos/t9008  well kinded application of an hk existential
  - neg/t9008  hk existential forbidden outside of type application
  - neg/t9008b kind error reported for hk existential

Regressed in 84d4671.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/files/pos/t9008.scala b/test/files/pos/t9008.scala
new file mode 100644
index 0000000000..d11b8604f2
--- /dev/null
+++ b/test/files/pos/t9008.scala
@@ -0,0 +1,5 @@
+trait Monad[M[_]]
+
+object Test {
+  def x: Monad[M forSome { type M[_] }] = ???
+}