mesa: Model INTEL perf query backend after query obj BE

mesa: Model INTEL perf query backend after query obj BE

Instead of using the same backend interface as AMD_performance_monitor
this defines a dedicated INTEL_performance_query interface that is
modelled more on the ARB_query_buffer_object interface (considering the
similarity of the extensions) with the addition of vfuncs for
initializing and enumerating query and counter info.

Compared to the previous backend, some notable differences are:

- The backend is free to represent counters using whatever data
  structures are optimal/convenient since queries and counters are
  enumerated via an iterator api instead of declaring them using
  structures directly shared with the frontend.

  This is also done to help us support the full range of data and
  semantic types available with INTEL_performance_query which is awkward
  while using a structure shared with the AMD_performance_monitor
  backend since neither extension's types are a subset of the other.

- The backend must support waiting for a query instead of the frontend
  simply using glFinish().

- Objects go through 'Active' and 'Ready' states consistent with the
  query object backend (hopefully making them more familiar). There is
  no 'Ended' state (which used to show that a query has ended at least
  once for a given object). There is a new 'Used' state, set when a
  query is first begun which implies that we are expecting to get
  results back for the object at some point. There's no equivalent to
  the 'EverBound' state since the spec doesn't require there to be a
  limbo state between generating IDs and associating them with an object
  on query Begin.

The INTEL_performance_query and AMD_performance_monitor extensions are
now completely orthogonal within Mesa main (though a driver could
optionally choose to implement both extensions within a unified backend
if that were convenient for the sake of sharing state/code).

v2: (Samuel Pitoiset)
- init PerfQuery.NumQueries in frontend
- s/return_string/output_clipped_string/
- s/backed/backend/ typo
- remove redundant *bytesWritten = 0
v3:
- Add InitPerfQueryInfo for lazy probing of available queries
v4:
- Clean up some internal usage of GL typedefs (Ken)

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>