This solves a problem where OpenXR timestamps could become invalid
(negative) in certain circumstances:
The timestamps that the OpenXR state tracker returned were offset such
that they appeared to start at OpenXR application startup time.
However monado-service is a long running service using system timestamps.
Because of this, if monado-service started work using a system timestamp
acquired before an OpenXR application started, then this system timestamp
could not be converted into an OpenXR without becoming invalid.
With this change, the OpenXR timestamps for OpenXR applications are offset
such that they appear to start at monado-service startup time instead.
As a side effect, all OpenXR applications connected to the same
monado-service instance will receive timestamps from the same domain.
This matches the OpenXR usage: the array is the plural of the element type,
and the count is the singular element type plus "count" (usually CountOutput
because of the two-call idiom)
Includes fixes to other code to match API changes.
Abandons the assumption that in oxr_system.xdevs[], index 0 is HMD,
1 is left controller, 2 is right controller.
Now to represent the dynamically assigned roles, oxr_system.role contains
the index for a device in oxr_system.xdevs[] for head, left and right.
This role assignment happens on the client side and currently can not be updated
from the server side.
Also adds an enum that device drivers set indicating allowed assignments
(many controllers are physically designed to be held in a specific hand).
This also adds support for configurations with only a HMD and a right controller.
