fix(svelte): infer props for generic Svelte components

[seroperson]

Closes #14669

Changes

When a Svelte component uses generic type parameters (<script generics="T extends ...">), the editor integration now preserves the generics in the generated TypeScript, so props are correctly inferred and intellisense works in .astro files.

Testing

Added several astro check tests in svelte/test/check.test.js

• Single-param generic with conditional type constraint
• Multi-param generic with nested angle brackets (Record<string, unknown>)
• Arrow function type in generic constraint ((val: string) => boolean)

To check this manually:

1. Create a Svelte component with generics attribute:

<script lang="ts" generics="T extends boolean = false">
  interface Props { flag?: T; items: T extends true ? number[] : string[] }
  let { flag, items }: Props = $props();
</script>

2. Import and use it in an .astro file
3. Before the fix: TypeScript errors and no intellisense
4. After the fix: props are correctly inferred with generic constraints

Docs

No docs changes are required.

[changeset-bot]

🦋 Changeset detected

Latest commit: de2dab0

The changes in this PR will be included in the next version bump.

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[seroperson]

VSCode e2e test just for the history