Improve some `wp-admin/includes/class-wp-filesystem-*.php` docs for `@param`.

See #30799.

Built from https://develop.svn.wordpress.org/trunk@30978


git-svn-id: http://core.svn.wordpress.org/trunk@30964 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Improve some docs for `@param`. Remove an unneeded `$wpdb` global import.

See #30799.

Built from https://develop.svn.wordpress.org/trunk@30979


git-svn-id: http://core.svn.wordpress.org/trunk@30965 1a063a9b-81f0-0310-95a4-ce76da25c4cd
In `wp_import_handle_upload()`:

`$file` was essentially getting declared/overwritten 3 times. In lieu of this, return an array containing the error immediately instead of doing a short-circuit array key assignment on error. Rename the local variable to `$upload` and use its properties instead of creating 3 new local vars, one of which stomped the array.

See #30799.

Built from https://develop.svn.wordpress.org/trunk@30980


git-svn-id: http://core.svn.wordpress.org/trunk@30966 1a063a9b-81f0-0310-95a4-ce76da25c4cd