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-foc/src/include/base/internal/lock_helper.h

@@ -48,7 +48,7 @@ static inline void thread_yield() { Fiasco::l4_thread_yield(); }
  *
  * \return true if the thread was in blocking state
  */
-static inline bool thread_check_stopped_and_restart(Genode::Thread_base *thread_base)
+static inline bool thread_check_stopped_and_restart(Genode::Thread *thread_base)
 {
 	Fiasco::l4_cap_idx_t tid = thread_base ?
 	                           thread_base->native_thread().kcap :
@@ -62,7 +62,7 @@ static inline bool thread_check_stopped_and_restart(Genode::Thread_base *thread_
 /**
  * Yield CPU time to the specified thread
  */
-static inline void thread_switch_to(Genode::Thread_base *thread_base)
+static inline void thread_switch_to(Genode::Thread *thread_base)
 {
 	Fiasco::l4_cap_idx_t tid = thread_base ?
 	                           thread_base->native_thread().kcap :
@@ -83,7 +83,7 @@ static void thread_stop_myself()
 {
 	using namespace Fiasco;
 
-	Genode::Thread_base *myself = Genode::Thread_base::myself();
+	Genode::Thread *myself = Genode::Thread::myself();
 	Fiasco::l4_cap_idx_t tid = myself ?
 	                           myself->native_thread().kcap :
 	                           Fiasco::MAIN_THREAD_CAP;