Fix #6152: dotc requires override to implement abstract java method

The reason is that bridges are allowed to participate in overriding
relationships. This commit does the same scalac does, that is,
prevent bridges from participation in such relationships.

Author: anatoliykmetyuk

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

@@ -731,6 +731,7 @@ object Flags {
   final val SyntheticTypeParam: FlagConjunction = allOf(Synthetic, TypeParam)
   final val SyntheticCase: FlagConjunction = allOf(Synthetic, Case)
   final val SyntheticOpaque: FlagConjunction = allOf(Synthetic, Opaque)
+  final val BridgeArtifact: FlagConjunction = allOf(Bridge, Artifact)
 
   implicit def conjToFlagSet(conj: FlagConjunction): FlagSet =
     FlagSet(conj.bits)

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

@@ -1141,7 +1141,7 @@ object SymDenotations {
      *  either as overrider or overridee.
      */
     final def memberCanMatchInheritedSymbols(implicit ctx: Context): Boolean =
-      !isConstructor && !is(Private)
+      !isConstructor && !is(Private) && !is(Artifact)
 
     /** The symbol, in class `inClass`, that is overridden by this denotation in class `siteClass`.*/
     final def overriddenSymbol(inClass: ClassSymbol, siteClass: ClassSymbol = owner.asClass)(implicit ctx: Context): Symbol =

compiler/src/dotty/tools/dotc/core/classfile/ClassfileConstants.scala

@@ -375,6 +375,6 @@ object ClassfileConstants {
     override def baseFlags(jflags: Int) = if ((jflags & JAVA_ACC_FINAL) == 0) Mutable else EmptyFlags
   }
   val methodTranslation: FlagTranslation = new FlagTranslation {
-    override def baseFlags(jflags: Int) = if ((jflags & JAVA_ACC_BRIDGE) != 0) Bridge else EmptyFlags
+    override def baseFlags(jflags: Int) = if ((jflags & JAVA_ACC_BRIDGE) != 0) (BridgeArtifact) else EmptyFlags
   }
 }

compiler/src/dotty/tools/dotc/transform/OverridingPairs.scala

@@ -40,7 +40,7 @@ object OverridingPairs {
      *  relative to <base>.this do
      */
     protected def matches(sym1: Symbol, sym2: Symbol): Boolean =
-      sym1.isType || self.memberInfo(sym1).matches(self.memberInfo(sym2))
+      sym1.isType || (!exclude(sym2) && self.memberInfo(sym1).matches(self.memberInfo(sym2)))
 
     /** The symbols that can take part in an overriding pair */
     private val decls = {