[Feature Request] Default value

[gm0124816]

First of all, thanks for the wonderful control !

It is common that you allow people to set a range for a value, but it is also common that a default value (within that range) must be selected. Currently two controls are needed to achieve this.

Is it possible to add a third thumb that can be moved within that range changing the 'default value' ? A little different style for that thumb would be recommended.

Avalonia is getting there, the only thing missing so far is the lack of available controls, especially controls like the one you guys created ! Your effort so far is very much appreciated and keep up the good work !