function getAllContexts() {
	const context_map = get_or_init_context_map('getAllContexts');
	return /** @type {T} */ (context_map);
}
Retrieves the whole context map that belongs to the closest parent component.
Must be called during component initialisation. Useful, for example, if you
programmatically create a component and want to pass the existing context to it.

@template {Map<any, any>} [T=Map<any, any>]
@returns {T}