feat: make transitions local by default

[dummdidumm]

BREAKING CHANGE: transitions are now local by default

This means that transitions are not played when they are nested within control flow blocks and a parent control flow block, not its immediate block, makes the element go away.

{#if x}
	{#if y}
		<!-- Svelte 3: <p transition:fade|local> -->
		<p transition:fade>
			fades in and out only when y changes
		</p>

		<!-- Svelte 3: <p transition:fade> -->
		<p transition:fade|global>
			fades in and out when x or y change
		</p>

	{/if}
{/if}

This solves a common gotcha with transitions interfering with page navigations.

To make them global, add the |global modifier:

-<div transition:fade>foo</div>
+<div transition:fade|global>foo</div>

closes #6686

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with npm test and lint the project with npm run lint

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Name	Status	Preview	Comments	Updated (UTC)
svelte-dev-2	❌ Failed (Inspect)			May 25, 2023 9:15am

[Rich-Harris]

we'll need to remember to update learn.svelte.dev when this is released

[dummdidumm]

Yes, we also need to update the current tutorial - I haven't got a good idea what to add there and how to make it so that people on version 3 still get the idea, but that's something for another PR.