[FIR] Report list of conflicting symbols in REDECLARATION and CONFLICTING_OVERLOADS

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -731,14 +731,18 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
     }
     add(FirErrors.CONFLICTING_OVERLOADS) { firDiagnostic ->
         ConflictingOverloadsImpl(
-            firDiagnostic.a,
+            firDiagnostic.a.map { abstractFirBasedSymbol ->
+                firSymbolBuilder.buildSymbol(abstractFirBasedSymbol.fir as FirDeclaration)
+            },
             firDiagnostic as FirPsiDiagnostic<*>,
             token,
         )
     }
     add(FirErrors.REDECLARATION) { firDiagnostic ->
         RedeclarationImpl(
-            firDiagnostic.a,
+            firDiagnostic.a.map { abstractFirBasedSymbol ->
+                firSymbolBuilder.buildSymbol(abstractFirBasedSymbol.fir as FirDeclaration)
+            },
             firDiagnostic as FirPsiDiagnostic<*>,
             token,
         )

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -521,12 +521,12 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
 
     abstract class ConflictingOverloads : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = ConflictingOverloads::class
-        abstract val conflictingOverloads: String
+        abstract val conflictingOverloads: List<KtSymbol>
     }
 
     abstract class Redeclaration : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = Redeclaration::class
-        abstract val conflictingDeclaration: String
+        abstract val conflictingDeclarations: List<KtSymbol>
     }
 
     abstract class AnyMethodImplementedInInterface : KtFirDiagnostic<PsiElement>() {

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -830,7 +830,7 @@ internal class ManyCompanionObjectsImpl(
 }
 
 internal class ConflictingOverloadsImpl(
-    override val conflictingOverloads: String,
+    override val conflictingOverloads: List<KtSymbol>,
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
 ) : KtFirDiagnostic.ConflictingOverloads(), KtAbstractFirDiagnostic<PsiElement> {
@@ -838,7 +838,7 @@ internal class ConflictingOverloadsImpl(
 }
 
 internal class RedeclarationImpl(
-    override val conflictingDeclaration: String,
+    override val conflictingDeclarations: List<KtSymbol>,
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
 ) : KtFirDiagnostic.Redeclaration(), KtAbstractFirDiagnostic<PsiElement> {