[all] Add changes

Author: x0k

.changeset/cool-snails-eat.md

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+---
+"@sjsf/sveltekit": patch
+"playground": patch
+"docs": patch
+---
+
+Migrate to `createForm3`

.changeset/ten-experts-compete.md

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+---
+"@sjsf/form": minor
+---
+
+Add `createForm3` function
+
+## Migration
+
+- Replace `useForm2` with `createForm3`.
+- If custom form is used it should call `setFormContext(form.context)` before using `FormContent` and `SubmitButton` components.