Set defTree properly

In the following test:

- tests/pos/i3130b.scala

If we add `transparent`, then everything is OK.
The reason is that we set `Symbol.defTree` systematically
in PostTyper. Now the inlining happens after PostTyper,
thus `defTree` is not properly set for inlined definitions.

To compensate, add ensure that `defTree` is set in the typer.
The inliner calls the typer, thus the inlined definitions will
have `defTree` set properly.

Author: liufengyun

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

@@ -2125,7 +2125,7 @@ class Typer extends Namer
       case rhs =>
         typedType(rhs)
     checkFullyAppliedType(rhs1)
-    assignType(cpy.TypeDef(tdef)(name, rhs1), sym)
+    assignType(cpy.TypeDef(tdef)(name, rhs1), sym).setDefTree
   }
 
   def typedClassDef(cdef: untpd.TypeDef, cls: ClassSymbol)(using Context): Tree = {
@@ -2265,7 +2265,7 @@ class Typer extends Namer
       for (deriver <- cdef.removeAttachment(AttachedDeriver))
         cdef1.putAttachment(AttachedDeriver, deriver)
 
-      cdef1
+      cdef1.setDefTree
     }
   }