Guild Wars 2

Will we get new additional button in the UI for using gliders and mastery skills and any other feature, so we dont have to go into inventory each time we want to use them?

Literally none of the revealed Mastery features are item-based or activated via the inventory. As demonstrated, they toggle on and stay on once unlocked and activate automatically under the correct circumstances.

So, no… there likely will be no UI buttons added.

The way to activate the glider is to be in the air and press the jump button after falling a certain distance (which can be shortened by higher levels of mastery). I don’t see the need for an extra UI button for it.