[MC-80823] fill command has wrong syntax help

The currently suggested syntax is:

/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [dataValue] [oldBlockHandling] [dataTag]

However based on ~~MC-61864~~, it should rather look like one of these:

/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [dataValue] [[oldBlockHandling] [dataTag]|[replace <TileName> [dataValue]]]

/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [dataValue] [oldBlockHandling] [dataTag] OR
/fill <x1> <y1> <z1> <x2> <y2> <z2> <TileName> [dataValue] replace <TileName> [dataValue]