FE: add test reproducing KT-54049

compiler/testData/diagnostics/tests/java8Overrides/falseManyImplementations.fir.kt

@@ -0,0 +1,13 @@
+abstract class ClassEmpty {
+    abstract fun foo()
+}
+
+interface BaseEmpty {
+    fun foo()
+}
+
+interface BaseDefault {
+    fun foo() {}
+}
+
+abstract <!MANY_IMPL_MEMBER_NOT_IMPLEMENTED!>class ClassEmpty_BaseEmpty_BaseDefault<!> : ClassEmpty(), BaseEmpty, BaseDefault

compiler/testData/diagnostics/tests/java8Overrides/falseManyImplementations.kt

@@ -0,0 +1,13 @@
+abstract class ClassEmpty {
+    abstract fun foo()
+}
+
+interface BaseEmpty {
+    fun foo()
+}
+
+interface BaseDefault {
+    fun foo() {}
+}
+
+abstract class ClassEmpty_BaseEmpty_BaseDefault : ClassEmpty(), BaseEmpty, BaseDefault

compiler/testData/diagnostics/tests/java8Overrides/falseManyImplementations.txt

@@ -0,0 +1,31 @@
+package
+
+public interface BaseDefault {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface BaseEmpty {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class ClassEmpty {
+    public constructor ClassEmpty()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public abstract fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public abstract class ClassEmpty_BaseEmpty_BaseDefault : ClassEmpty, BaseEmpty, BaseDefault {
+    public constructor ClassEmpty_BaseEmpty_BaseDefault()
+    public open override /*3*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*3*/ /*fake_override*/ fun foo(): kotlin.Unit
+    public open override /*3*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*3*/ /*fake_override*/ fun toString(): kotlin.String
+}