[kernel] Move more from kutil to kernel

The moving of kernel-only code out of kutil continues. (See 042f061)
This commit moves the following:

- The heap allocator code
- memory.cpp/h which means:
  - letting string.h be the right header for memset and memcpy, still
    including an implementation of it for the kernel though, since
    we're not linking libc to the kernel
  - Changing calls to kalloc/kfree to new/delete in kutil containers
    that aren't going to be merged into the kernel
- Fixing a problem with stdalign.h from libc, which was causing issues
  for type_traits.

src/kernel/objects/thread.cpp

@@ -1,6 +1,8 @@
 #include "j6/signals.h"
+
 #include "cpu.h"
 #include "log.h"
+#include "memory.h"
 #include "objects/thread.h"
 #include "objects/process.h"
 #include "objects/vm_area.h"
@@ -40,7 +42,7 @@ thread::from_tcb(TCB *tcb)
 {
     static ptrdiff_t offset =
         -1 * static_cast<ptrdiff_t>(offsetof(thread, m_tcb));
-    return reinterpret_cast<thread*>(kutil::offset_pointer(tcb, offset));
+    return reinterpret_cast<thread*>(offset_pointer(tcb, offset));
 }
 
 thread & thread::current() { return *current_cpu().thread; }