Thread API cleanup

This patch cleans up the thread API and comes with the following
noteworthy changes:

- Introduced Cpu_session::Weight type that replaces a formerly used
  plain integer value to prevent the accidental mix-up of
  arguments.
- The enum definition of Cpu_session::DEFAULT_WEIGHT moved to
  Cpu_session::Weight::DEFAULT_WEIGHT
- New Thread constructor that takes a 'Env &' as first argument.
  The original constructors are now marked as deprecated. For the
  common use case where the default 'Weight' and 'Affinity' are
  used, a shortcut is provided. In the long term, those two
  constructors should be the only ones to remain.
- The former 'Thread<>' class template has been renamed to
  'Thread_deprecated'.
- The former 'Thread_base' class is now called 'Thread'.
- The new 'name()' accessor returns the thread's name as 'Name'
  object as centrally defined via 'Cpu_session::Name'. It is meant to
  replace the old-fashioned 'name' method that takes a buffer and size
  as arguments.
- Adaptation of the thread test to the new API

Issue #1954

repos/base-nova/include/nova/util.h

@@ -33,7 +33,7 @@ inline void request_event_portal(Genode::Native_capability const &cap,
                                  Genode::addr_t sel, Genode::addr_t event,
                                  unsigned short log2_count = 0)
 {
-	Genode::Thread_base * myself = Genode::Thread_base::myself();
+	Genode::Thread * myself = Genode::Thread::myself();
 	Nova::Utcb *utcb = reinterpret_cast<Nova::Utcb *>(myself->utcb());
 
 	/* save original receive window */
@@ -73,7 +73,7 @@ inline void request_signal_sm_cap(Genode::Native_capability const &cap,
 inline void delegate_vcpu_portals(Genode::Native_capability const &cap,
                                   Genode::addr_t const sel)
 {
-	Genode::Thread_base * myself = Genode::Thread_base::myself();
+	Genode::Thread * myself = Genode::Thread::myself();
 	Nova::Utcb *utcb = reinterpret_cast<Nova::Utcb *>(myself->utcb());
 
 	/* save original receive window */