[FIR] Implement INVALID_CHARACTERS

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

@@ -2876,6 +2876,13 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.INVALID_CHARACTERS) { firDiagnostic ->
+        InvalidCharactersImpl(
+            firDiagnostic.a,
+            firDiagnostic as FirPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.EQUALITY_NOT_APPLICABLE) { firDiagnostic ->
         EqualityNotApplicableImpl(
             firDiagnostic.a,

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

@@ -2011,6 +2011,11 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = UnderscoreUsageWithoutBackticks::class
     }
 
+    abstract class InvalidCharacters : KtFirDiagnostic<KtNamedDeclaration>() {
+        override val diagnosticClass get() = InvalidCharacters::class
+        abstract val message: String
+    }
+
     abstract class EqualityNotApplicable : KtFirDiagnostic<KtBinaryExpression>() {
         override val diagnosticClass get() = EqualityNotApplicable::class
         abstract val operator: String

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

@@ -3239,6 +3239,14 @@ internal class UnderscoreUsageWithoutBackticksImpl(
     override val firDiagnostic: FirPsiDiagnostic by weakRef(firDiagnostic)
 }
 
+internal class InvalidCharactersImpl(
+    override val message: String,
+    firDiagnostic: FirPsiDiagnostic,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.InvalidCharacters(), KtAbstractFirDiagnostic<KtNamedDeclaration> {
+    override val firDiagnostic: FirPsiDiagnostic by weakRef(firDiagnostic)
+}
+
 internal class EqualityNotApplicableImpl(
     override val operator: String,
     override val leftType: KtType,