Mouse Button Modifiers naming convention

[blyedev]

Back in 2017 the pr vuejs/vue#7069 proposed renaming the mouse button modifiers to primary, secondary and auxiliary which was approved but also delayed to a future version to avoid deprecation inbetween versions. That however never happened.

Firstly I would like to ask if this is simply because the pr has been forgotten about or was there a blocker?
Secondly if this is something that's still desired I would like to propose to extend the selection by the 4th and 5th button, keeping in line with what's actually availible under the event buttons property as defined in here