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-linux/src/test/lx_hybrid_errno/main.cc

@@ -17,12 +17,12 @@
 
 enum { STACK_SIZE = 4096 };
 
-struct Thread : Genode::Thread<STACK_SIZE>
+struct Thread : Genode::Thread_deprecated<STACK_SIZE>
 {
 	Genode::Lock &_barrier;
 
 	Thread(Genode::Lock &barrier)
-	: Genode::Thread<STACK_SIZE>("stat"), _barrier(barrier) { start(); }
+	: Genode::Thread_deprecated<STACK_SIZE>("stat"), _barrier(barrier) { start(); }
 
 	void entry()
 	{

repos/base-linux/src/test/lx_hybrid_pthread_ipc/main.cc

@@ -34,11 +34,11 @@ static void *pthread_entry(void *)
 	PINF("first message");
 
 	/*
-	 * Without the lazy initialization of 'Thread_base' objects for threads
+	 * Without the lazy initialization of 'Thread' objects for threads
 	 * created w/o Genode's Thread API, the printing of the first message will
 	 * never return because the IPC reply could not be delivered.
 	 *
-	 * With the on-demand creation of 'Thread_base' objects, the second message
+	 * With the on-demand creation of 'Thread' objects, the second message
 	 * will appear in the LOG output.
 	 */
 

repos/base-linux/src/test/lx_rmap/main.cc

@@ -44,7 +44,7 @@ int main()
 	using namespace Genode;
 
 	/* activate for early printf in Rm_session_mmap::attach() etc. */
-	if (0) Thread_base::trace("FOO");
+	if (0) Thread::trace("FOO");
 
 	/* induce initial heap expansion to remove RM noise */
 	if (1) {