Filesystem API: Fix inaccurate WP_Filesystem_Direct::chmod() file permissions comparison

[jeremyfelt]

The use of | 0644 alters the permission bits read from the file to a minimum floor before comparing them with the requested mode.

This results in an inaccurate comparison.

Removing this allows the & 0777 mask to perform as intended: strip the filetype bits from the value returned by fileperms( $file ) so that the current permission bits can be used for comparison with the requested mode.

This was added during review as part of #64610 for consistency with other parts of core, but those are using | 0755 and | 0644 to ensure FS_CHMOD_DIR and FS_CHMOD_FILE are set with the minimum permission bits required.

Trac ticket: https://core.trac.wordpress.org/ticket/65695

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