feat: Reset form programmatically

[sillvva]

fixes #14754
fixes #14210

Implements a form.reset() method that clears the form values, issues, result, submitted, and touched states. In addition, the dev is provided options to not reset certain parts, and the ability to reset the form to new values.

Includes SSR support, so the dev could also use form.reset({ values: { ... } }) in the script block instead of form.fields.set({ ... }) if they wanted to. One advantage is that it allows a DeepPartial<Input> type, instead of requiring the whole object. Unlike .set() this method is only for the base path.

Demo

export type RemoteForm<Input extends RemoteFormInput | void, Output> = {
	...
	/** Reset the form to its initial state */
	reset(options?: {
		/**
		 * Set this to the new values to reset the form to.
		 * Set this to `false` to not reset the values.
		 * @default true
		 */
		values?: DeepPartial<Input> | boolean;
		/** Set this to `false` to not reset the issues. */
		issues?: boolean;
		/** Set this to `false` to not reset the result. */
		result?: boolean;
		/** Set this to `false` to not reset the touched fields. */
		touched?: boolean;
	}): void;
};

It does provide an alternative solution to this issue too:

When navigating to a new page and back on the client, the values (input), issues, and result are not reset. Looking into this, I see that the instance is only deleted on submit if the form has a key from .for(key). This PR would give developers the ability to reset without using .for().

---

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🦋 Changeset detected

Latest commit: 8562ffd

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

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Name	Type
@sveltejs/kit	Minor

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-14779-svelte.vercel.app/