MediaUploader::upload() triggers undefined array key notice for max_resolution causing upload failures

Problem
When using the Gutenberg media uploader, uploading a file can result in a NotFoundHttpException (or other errors depending on error handling/logging configuration). This happens because MediaUploader.php uses the ternary shorthand operator (?:) on $file_settings['max_resolution']:

PHP
$image_settings['max_dimensions'] = $file_settings['max_resolution'] ?: $image_settings['max_dimensions'];

If the max_resolution key is not present in the $file_settings array, PHP raises an Undefined array key warning/notice. In environments where notices are strictly handled or logged/suppressed via custom error handlers, this breaks the media upload flow.

Proposed Solution
Replace the ternary shorthand operator (?:) with the null-coalescing operator (??), which safely checks for the existence and null-status of the key without triggering an undefined index notice:

PHP
$image_settings['max_dimensions'] = $file_settings['max_resolution'] ?? $image_settings['max_dimensions'];

Steps to Reproduce
Attempt a media upload through the Gutenberg editor where $file_settings does not explicitly define a max_resolution key.

Observe the PHP notice / subsequent exception preventing a successful upload response.

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