State: Autosave should be treated as regular save for same-user draft post

[aduth]

Related: #7122 (comment)

When an autosave occurs for an auto-draft or draft post authored by the same user, the server treats it as a regular save:

gutenberg/lib/class-wp-rest-autosaves-controller.php

Lines 182 to 185 in 7141ce6

	if ( ( 'draft' === $post->post_status || 'auto-draft' === $post->post_status ) && $post->post_author == $user_id ) {
	// Draft posts for the same author: autosaving updates the post and does not create a revision.
	// Convert the post object to an array and add slashes, wp_update_post expects escaped array.
	$autosave_id = wp_update_post( wp_slash( (array) $prepared_post ), true );

This should also be respected in the client, meaning:

• There should be no prompts for unsaved changes after this occurs
• The post's "current" values, i.e. state.currentPost, should reflect anything included in the autosave request

A couple possible implementations may include:

• Testing as a condition of the save effect to consider isAutosave as false when the autosave is draft for current user
• Handling as a case in the currentPost reducer
• Dispatch resetPost after autosave completes successfully, when autosave is draft for current user