Retain transparent flag on exports

Fixes #12958

Author: odersky

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

@@ -531,7 +531,7 @@ object Flags {
   val RetainedModuleClassFlags: FlagSet = RetainedModuleValAndClassFlags | Enum
 
   /** Flags retained in export forwarders */
-  val RetainedExportFlags = Given | Implicit | Inline
+  val RetainedExportFlags = Given | Implicit | Inline | Transparent
 
   /** Flags that apply only to classes */
   val ClassOnlyFlags = Sealed | Open | Abstract.toTypeFlags

tests/pos/i12958.scala

@@ -0,0 +1,17 @@
+import scala.quoted.*
+
+package mylib:
+  object Export:
+    transparent inline def exported: Any = 1
+
+  object Import:
+    transparent inline def imported: Any = 1
+
+  export Export.*
+
+
+import mylib.*
+import Import.*
+object Test:
+  val oneFail : 1 = exported //error
+  val oneWork : 1 = imported //works