Revert changes to CheckRealizable

Since Shape is no longer generated separately we do not need to make
an exception for synthesized members.

Author: odersky

compiler/src/dotty/tools/dotc/core/CheckRealizable.scala

@@ -111,11 +111,7 @@ class CheckRealizable(implicit ctx: Context) {
   /** `Realizable` if `tp` has good bounds, a `HasProblem...` instance
    *  pointing to a bad bounds member otherwise. "Has good bounds" means:
    *
-   *    - all non-synthetic type members have good bounds.
-   *      Synthetic members are unchecked, for two reasons:
-   *       - synthetic opaque aliases do have conflicting bounds, but this is OK
-   *       - we should not force synthesized Shape types because that might
-   *         query the `children` annotation too early.
+   *    - all type members have good bounds (except for opaque helpers)
    *    - all refinements of the underlying type have good bounds (except for opaque companions)
    *    - all base types are class types, and if their arguments are wildcards
    *      they have good bounds.
@@ -133,8 +129,7 @@ class CheckRealizable(implicit ctx: Context) {
     val memberProblems =
       for {
         mbr <- tp.nonClassTypeMembers
-        if !mbr.symbol.is(Synthetic)
-        if !(mbr.info.loBound <:< mbr.info.hiBound)
+        if !(mbr.info.loBound <:< mbr.info.hiBound) && !mbr.symbol.isOpaqueHelper
       }
       yield new HasProblemBounds(mbr.name, mbr.info)