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/include/cpu_session/client.h

@@ -26,9 +26,9 @@ struct Genode::Cpu_session_client : Rpc_client<Cpu_session>
 	: Rpc_client<Cpu_session>(session) { }
 
 	Thread_capability
-	create_thread(Capability<Pd_session> pd, size_t quota, Name const &name,
-	              Affinity::Location affinity, addr_t utcb = 0) override {
-		return call<Rpc_create_thread>(pd, quota, name, affinity, utcb); }
+	create_thread(Capability<Pd_session> pd, Name const &name,
+	              Affinity::Location affinity, Weight weight, addr_t utcb = 0) override {
+		return call<Rpc_create_thread>(pd, name, affinity, weight, utcb); }
 
 	Ram_dataspace_capability utcb(Thread_capability thread) override {
 		return call<Rpc_utcb>(thread); }