feat(html/svelte): if/else syntax (#8031)

Co-authored-by: dyc3 <[email protected]>

Author: ematipico

.changeset/spicy-actors-leave.md

@@ -0,0 +1,22 @@
+---
+"@biomejs/biome": patch
+---
+
+Added support for the Svelte syntax `{#if}{/if}`. The Biome HTML parser is now able to parse and format the [`{#if}{/if} blocks`](https://svelte.dev/docs/svelte/if):
+
+```diff
+<!-- if / else-if / else -->
+{#if porridge.temperature > 100}
+-<p>too hot!</p>
++  <p>too hot!</p>
+{:else if 80 > porridge.temperature}
+-<p>too cold!</p>
++  <p>too cold!</p>
+{:else if 100 > porridge.temperature}
+-<p>too too cold!</p>
++  <p>too too cold!</p>
+{:else}
+-<p>just right!</p>
++  <p>just right!</p>
+{/if}
+```