[Wasm] Fix unit issues

- Materialize unit when its value is actually needed.
- Special-case Unit_getInstance return type at codegen. It should be a
  proper Unit object instead of a "void"

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InlineClassDeclarationLowering.kt

@@ -156,6 +156,8 @@ class InlineClassLowering(val context: CommonBackendContext) {
                         +statement.transformStatement(object : IrElementTransformerVoid() {
                             override fun visitDelegatingConstructorCall(expression: IrDelegatingConstructorCall): IrExpression {
                                 expression.transformChildrenVoid()
+                                // Static function for delegating constructors return unboxed instance of inline class
+                                expression.type = irClass.defaultType
                                 return irBlock(expression) {
                                     thisVar = createTmpVariable(
                                         expression,