[fix] make Source type in preprocess private (#6726)

Is only used internally, shouldn't be exposed. Fixes #6622

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Svelte changelog
 
+## Unreleased
+
+* Hide private preprocess typings ([#6622](https://github.com/sveltejs/svelte/issues/6622))
+
 ## 3.42.5
 
 * In `draw` transition, account for `stroke-linecap` in determining length ([#4540](https://github.com/sveltejs/svelte/issues/4540))

src/compiler/preprocess/types.ts

@@ -1,5 +1,8 @@
 import { Location } from 'locate-character';
 
+/**
+ * @internal
+ */
 export interface Source {
 	source: string;
 	get_location: (search: number) => Location;