Fix bug where server side upload errors disappear automatically

[jorgefilipecosta]

Fixes: #7372
Partially reverts: #6957

Unfortunately, the approach used in #6957 to add upload error messages to all blocks without changing them does not seems possible, it created a regression as described in #6957, props to @danielbachhuber for catching this bug.

What happens is that when we upload we create a temporary blob URL for the file so that the placeholder disappears and the uploaded file appears immediately. In this case, the placeholder is unmounted. If we get an error message from the server e.g.: not something we can validate on the client, we set an error message but the placeholder is already not visible. Then a new placeholder is rendered, but its state is empty and the error message we set is not used anywhere.
This makes impossible to handle the notices in the media placeholder and forces them to be managed at the block level.

This PR does the following changes:
Reverts the changes by #6957 in the gallery, image, and media-placeholder.

Adds upload error notices to video, audio and cover image.

Solves an existing bug in the video, audio, and cover image blocks where if the upload failed, we continued with a blob URL set.

How has this been tested?

I added the following blocks with empty placeholders: video, audio, image, gallery, and cover-image.

For each of them, I uploaded a file with success. In audio block, it was not possible to upload mp3 files, but wav files were ok. I got the error message implemented in #6968. This happens because of a google chrome bug where audio/mp3 mimetype is used for audio instead of the correct one audio/mpeg. More info in :https://bugs.chromium.org/p/chromium/issues/detail?id=227004. I added a work around in #7398.

I added the following test code that forces server side upload errors:

$force_upload_failure = function( $file ) {
	$file['error'] = 'This file upload has been forced to fail.';
	return $file;
};
add_filter( 'wp_handle_sideload_prefilter', $force_upload_failure );
add_filter( 'wp_handle_upload_prefilter', $force_upload_failure );

I tried to upload to all the blocks and verified an error correctly appears on the block placeholder.

I change the max upload error size of my test site using htaccess:

php_value upload_max_filesize 3M
php_value post_max_size 3M

Tried to upload files bigger than 3M to all the blocks and verified a max file size error message appeared correctly.

[danielbachhuber]

👍 Works in my testing.