Support for object-rest in each destructuring

[mindrones]

It'd be nice to be able to do:

{#each sections as {type, ...props}}
  <svelte:component this={foo[type]} {...props} />
{/each}

as an alternative to:

{#each sections as section}
  <svelte:component this={foo[section.type]} {...section} />
{/each}

[EmilTholin]

That would be really nice. I think it can be supported by extending read_context to understand the rest syntax and extending unpack_desctructuring to take a new RestPattern into consideration.

A new Bublé-esque objectWithoutProperties helper function might be needed.