fix in transition when tag of <svelte:element> changed

src/compiler/compile/render_dom/wrappers/Element/index.ts

@@ -298,6 +298,7 @@ export default class ElementWrapper extends Wrapper {
 				${this.var}.d(1);
 				${this.var} = ${this.child_dynamic_element_block.name}(#ctx);
 				${this.var}.c();
+				@transition_in(${this.var});
 				this.m(${this.get_update_mount_node(anchor)}, ${anchor});
 			} else {
 				${this.var}.p(#ctx, #dirty);

test/runtime/samples/dynamic-element-transition-css-change-tag/_config.js

@@ -0,0 +1,14 @@
+export default {
+	test({ assert, component, target, raf }) {
+		component.visible = true;
+		const h1 = target.querySelector('h1');
+
+		assert.equal(h1.style.animation, '__svelte_3809512021_0 100ms linear 0ms 1 both');
+
+		raf.tick(50);
+		component.tag = 'h2';
+		const h2 = target.querySelector('h2');
+		assert.equal(h1.style.animation, '__svelte_3809512021_0 100ms linear 0ms 1 both');
+		assert.equal(h2.style.animation, '__svelte_3809512021_0 100ms linear 0ms 1 both');
+	}
+};

test/runtime/samples/dynamic-element-transition-css-change-tag/main.svelte

@@ -0,0 +1,17 @@
+<script>
+	export let tag = "h1";
+	export let visible;
+
+	function foo() {
+		return {
+			duration: 100,
+			css: t => {
+				return `opacity: ${t}`;
+			}
+		};
+	}
+</script>
+
+{#if visible}
+	<svelte:element this={tag} in:foo></svelte:element>
+{/if}