Support a mechanism to suspend layout when appending lots of children to a node (createDocumentFragment).

[dtzxporter]

Describe the problem

Right now, when managing a list using an {#each} block, a lot of the frame is taken up by layout recalculating every time a appendChild fires (Lazily loading more items as you scroll).

Describe the proposed solution

Some way to have svelte automatically create a document fragment, append the newly created nodes to that fragment, then, append the fragment itself as the child so that layout calculation only has to happen one time.

Alternatives considered

Manually doing it and component registration / destruction, but this can be messy and uses internal apis.

Importance

would make my life easier

[dummdidumm]

Svelte 5 is more efficient in this regard, namely using document fragments under the hood and thereby reduing the number of appends, therefore closing.