fix(print): handle svelte:body and fix keyframe percentage double-printing (#18234)

Fixes #18206 and fixes #18207 — both are printer bugs in
`packages/svelte/src/compiler/print/index.js`.

## Changes

### Fix 1: `svelte:body` crashes the printer (#18206)

`SvelteBody` was missing from the visitor map, causing a crash with
`Error: Not implemented: SvelteBody`. Added the handler (same one-liner
pattern as `SvelteDocument`, `SvelteHead`, etc.) and added `SvelteBody`
to the `is_block_element` check so whitespace is handled consistently.

### Fix 2: Keyframe percent stops print as `0%%` (#18207)

`Percentage.value` already includes the `%` sign (captured by
`/\d+(\.\d+)?%/y`), but the printer was writing `` `${node.value}%` `` —
appending a second `%`. Changed to `context.write(node.value)` to match
the `Nth` printer pattern directly above it.

Also updated the existing `style` snapshot which had `50%%` (the bug was
silently baked in), and added dedicated test samples for both fixes.

.changeset/fix-printer-svelte-body-keyframe-percent.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix(print): handle `svelte:body` and fix keyframe percentage double-printing

packages/svelte/src/compiler/print/index.js

@@ -247,7 +247,7 @@ const css_visitors = {
 	},
 
 	Percentage(node, context) {
-		context.write(`${node.value}%`);
+		context.write(node.value);
 	},
 
 	PseudoClassSelector(node, context) {
@@ -417,6 +417,7 @@ const svelte_visitors = (comments) => ({
 				const is_block_element =
 					child_node.type === 'RegularElement' ||
 					child_node.type === 'Component' ||
+					child_node.type === 'SvelteBody' ||
 					child_node.type === 'SvelteHead' ||
 					child_node.type === 'SvelteFragment' ||
 					child_node.type === 'SvelteBoundary' ||
@@ -821,6 +822,10 @@ const svelte_visitors = (comments) => ({
 		context.write('</style>');
 	},
 
+	SvelteBody(node, context) {
+		base_element(node, context, comments);
+	},
+
 	SvelteBoundary(node, context) {
 		base_element(node, context, comments);
 	},

packages/svelte/tests/print/samples/css-keyframes-percent/input.svelte

@@ -0,0 +1,7 @@
+<style>
+  @keyframes foo {
+    0% { left: 0px; }
+    50% { left: 50px; }
+    100% { left: 100px; }
+  }
+</style>

packages/svelte/tests/print/samples/css-keyframes-percent/output.svelte

@@ -0,0 +1,13 @@
+<style>
+	@keyframes foo {
+		0% {
+			left: 0px;
+		}
+		50% {
+			left: 50px;
+		}
+		100% {
+			left: 100px;
+		}
+	}
+</style>

packages/svelte/tests/print/samples/style/output.svelte

@@ -19,7 +19,7 @@
 		from {
 			opacity: 0;
 		}
-		50%% {
+		50% {
 			opacity: 0.5;
 		}
 		to {

packages/svelte/tests/print/samples/svelte-body/input.svelte

@@ -0,0 +1 @@
+<svelte:body onmousemove={handleMousemove} />

packages/svelte/tests/print/samples/svelte-body/output.svelte

@@ -0,0 +1 @@
+<svelte:body onmousemove={handleMousemove}></svelte:body>