[IR] Implement new IrSymbol API

- Add predicate whether symbol is PublicAPI
 - Split symbols into 2 types (Public/Private)
 - Fix special implementations

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/WasmBackendContext.kt

@@ -24,8 +24,8 @@ import org.jetbrains.kotlin.ir.symbols.IrExternalPackageFragmentSymbol
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
 import org.jetbrains.kotlin.ir.symbols.impl.IrExternalPackageFragmentSymbolImpl
+import org.jetbrains.kotlin.ir.util.IdSignature
 import org.jetbrains.kotlin.ir.util.SymbolTable
-import org.jetbrains.kotlin.ir.util.UniqId
 import org.jetbrains.kotlin.name.FqName
 
 class WasmBackendContext(
@@ -90,15 +90,17 @@ class DescriptorlessExternalPackageFragmentSymbol : IrExternalPackageFragmentSym
     private var _owner: IrExternalPackageFragment? = null
     override val owner get() = _owner!!
 
-    override var uniqId: UniqId
-        get() = error("Operation is unsupported")
-        set(value) { error("Operation is unsupported") }
-
     override val isBound get() = _owner != null
 
     override fun bind(owner: IrExternalPackageFragment) {
         _owner = owner
     }
+
+    override val isPublicApi: Boolean
+        get() = error("Operation is unsupported")
+
+    override val signature: IdSignature
+        get() = error("Operation is unsupported")
 }