Initialize select element value upon creation of component.

[taylorzane]

This PR fixes an issue where a select element is not set to the correct value on the initial creation of a component.

Mainly done in response to @saibotsivad, but I have also experienced this behavior when writing Svelte components with select elements.

This snippet simply forces the select item to update after the each_block has been rendered, allowing select.value to be set.

I have not included the test that @saibotsivad created to prevent plagiarism.

/cc @saibotsivad

[Rich-Harris]

Thanks both! I pulled in @saibotsivad's test, so this should stay fixed. Will cut a release shortly

[saibotsivad]

You two rock, thanks!