[Wasm] NFC refactor: eraseGenerics -> toWasmSignatureType

Use a more concrete name, make it private,
and split out:

 IrSimpleType.toWasmSignatureSimpleType

This does not change the behavior,
but helps to set the stage for the following bugfix
 (KT-58852)

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/utils/TypeTranformer.kt

@@ -13,13 +13,6 @@ import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.defaultType
 
-fun IrType.eraseGenerics(irBuiltIns: IrBuiltIns): IrType {
-    if (this is IrDynamicType) return this
-    if (this is IrErrorType) return this
-    val defaultType = this.erasedUpperBound?.defaultType ?: irBuiltIns.anyType
-    if (!this.isNullable()) return defaultType
-    return defaultType.makeNullable()
-}
 
 // Return null if upper bound is Any
 private val IrTypeParameter.erasedUpperBound: IrClass?

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/ir2wasm/ClassInfo.kt

@@ -5,21 +5,17 @@
 
 package org.jetbrains.kotlin.backend.wasm.ir2wasm
 
-import org.jetbrains.kotlin.ir.util.isOverridableOrOverrides
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.ir.IrBuiltIns
-import org.jetbrains.kotlin.ir.backend.js.utils.eraseGenerics
+import org.jetbrains.kotlin.ir.backend.js.utils.erasedUpperBound
 import org.jetbrains.kotlin.ir.backend.js.utils.realOverrideTarget
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
-import org.jetbrains.kotlin.ir.types.IrType
-import org.jetbrains.kotlin.ir.types.classifierOrFail
-import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
-import org.jetbrains.kotlin.ir.util.isInterface
-import org.jetbrains.kotlin.ir.util.render
+import org.jetbrains.kotlin.ir.types.*
+import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.Name
 
 data class WasmSignature(
@@ -45,12 +41,23 @@ data class WasmSignature(
 fun IrSimpleFunction.wasmSignature(irBuiltIns: IrBuiltIns): WasmSignature =
     WasmSignature(
         name,
-        extensionReceiverParameter?.type?.eraseGenerics(irBuiltIns),
-        valueParameters.map { it.type.eraseGenerics(irBuiltIns) },
-        returnType.eraseGenerics(irBuiltIns),
+        extensionReceiverParameter?.type?.toWasmSignatureType(irBuiltIns),
+        valueParameters.map { it.type.toWasmSignatureType(irBuiltIns) },
+        returnType.toWasmSignatureType(irBuiltIns),
         isOverridableOrOverrides
     )
 
+private fun IrType.toWasmSignatureType(irBuiltIns: IrBuiltIns): IrType =
+    when (this) {
+        is IrSimpleType -> toWasmSignatureSimpleType(irBuiltIns)
+        else -> this
+    }
+
+private fun IrSimpleType.toWasmSignatureSimpleType(irBuiltIns: IrBuiltIns): IrSimpleType {
+    val klass = (this.erasedUpperBound?.symbol ?: irBuiltIns.anyClass).owner
+    return klass.defaultType.withNullability(this.isNullable())
+}
+
 class VirtualMethodMetadata(
     val function: IrSimpleFunction,
     val signature: WasmSignature

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/types/irTypes.kt

@@ -31,7 +31,7 @@ private fun IrType.withNullability(newNullability: Boolean): IrType =
         else -> this
     }
 
-private fun IrSimpleType.withNullability(newNullability: Boolean): IrSimpleType {
+fun IrSimpleType.withNullability(newNullability: Boolean): IrSimpleType {
     val requiredNullability = if (newNullability) SimpleTypeNullability.MARKED_NULLABLE else SimpleTypeNullability.DEFINITELY_NOT_NULL
     return if (nullability == requiredNullability)
         this