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.
Many functions returned void and were assumed to always succeed, and some functions
returned only a bool to indicate vague success/failure.
Now that these functions get piped over IPC all of them have to be able to indicate
an IPC failure like for example an unreachable service.
With the xrt_result_t return type they now have the opportunity to report various
types of failures.
Functions down the line should be able to fail and return a status.
They can be called either through IPC or directly depending on compile settings,
therefore we need an internal result type for various XR_ERROR_* errors, but also IPC failure.
For now functions in ipc_client_utils.c only return XRT_SUCCESS or XRT_ERROR_IPC_FAILURE.
If there is no IPC failure, the generated protocol will extract and return the called functions'
actual return value from the reply.
v2: make failure results negative
Store Thumbstick, Trackpad etc. data internally in a vec2f.
The knowledge that a binding path ../x and ../y refers to the x and y components of this vec2f
is stored as an INPUT_REDIRECT_VEC2_X_TO_VEC1 or INPUT_REDIRECT_VEC2_Y_TO_VEC enum.
Actions now also store the index of the binding paths it matched to,
e.g. when an action binds ../trackpad/y to an input that provides bindings [../trackpad, ../trackpad/x, ../trackpad/y],
the index 2 is stored.
v2: Clarify preferred binding path index variable
