Svelte5: Add `svelte/no-legacy-svelte-ignore` rule

[ota-meshi]

Motivation

Svelte v5 changed the format of error codes to snake_case, but svelte-ignore still works for the previous kebab-case error codes.
However, I expect support for the old format will be removed eventually.
The new rule help with this migration.

Description

The new rule disallow svelte-ignore using old-style error codes.
Note, however, that they will only be reported if you are using Svelte v5 or later.

Examples

<!-- ✓ GOOD -->
<!-- svelte-ignore a11y_no_noninteractive_tabindex -->
<span tabindex="0">
	<span class="element"></span>
</span>
<div>
	<!-- svelte-ignore block_empty -->
	{#await Promise.resolve(foo)}
	{/await}
</div>

<!-- ✗ BAD -->
<!-- svelte-ignore a11y-no-noninteractive-tabindex -->
<span tabindex="0">
	<span class="element"></span>
</span>
<div>
	<!-- svelte-ignore empty-block -->
	{#await Promise.resolve(foo)}
	{/await}
</div>

Additional comments

No response