xkb: XkbAssembleMap() use explicit parameters instead of struct

[metux]

Don't pass in the reply header struct anymore, instead only pass the individual values that we really need here.

[algrid]

Why do you think it's better? The old version looks more compact.

[ONykyf]

Probability of error, e.g., incorrect fields order, increases.

[b-aaz]

The old one looks better. This new function is reeealy long.