Disallow context function types as value-class parameters

[Cherry-picked 3ee5b29]

Author: bracevac

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -755,6 +755,8 @@ object Checking {
         }
         clParamAccessors match {
           case param :: params =>
+            if (defn.isContextFunctionType(param.info))
+              report.error("value classes are not allowed for context function types", param.srcPos)
             if (param.is(Mutable))
               report.error(ValueClassParameterMayNotBeAVar(clazz, param), param.srcPos)
             if (param.info.isInstanceOf[ExprType])

tests/neg/i22752.scala

@@ -0,0 +1,4 @@
+class Inner(body: Int ?=> Int) extends AnyVal: // error
+  def rescue: Int ?=> Int = ???
+
+class Inner2(body: Int => Int) extends AnyVal // ok