[kernel] Spit out vm_area types

The vm_space allow() functionality was a bit janky; using VMAs for all
regions would be a lot cleaner. To that end, this change:

- Adds a "static array" ctor to kutil::vector for setting the kernel
  address space's VMA list. This way a kernel heap VMA can be created
  without the heap already existing.
- Splits vm_area into different subclasses depending on desired behavior
- Splits out the concept of vm_mapper which maps vm_areas to vm_spaces,
  so that some kinds of VMA can be inherently single-space
- Implements VMA resizing so that userspace can grow allocations.
- Obsolete page_table_indices is removed

Also, the following bugs were fixed:

- kutil::map iterators on empty maps no longer break
- memory::page_count was doing page-align, not page-count

See: Github bug #242
See: [frobozz blog post](https://jsix.dev/posts/frobozz/)

Tags:

src/include/kernel_memory.h

@@ -17,7 +17,7 @@ namespace memory {
 	constexpr uintptr_t page_offset = 0xffffc00000000000ull;
 
 	/// Max number of pages for a kernel stack
-	constexpr unsigned kernel_stack_pages = 1;
+	constexpr unsigned kernel_stack_pages = 4;
 
 	/// Max number of pages for a kernel buffer
 	constexpr unsigned kernel_buffer_pages = 16;
@@ -62,6 +62,6 @@ namespace memory {
 	/// \arg bytes  The number of bytes desired
 	/// \returns    The number of pages needed to contain the desired bytes
 	inline size_t page_count(size_t bytes) {
-		return ((bytes - 1) & (frame_size - 1)) + 1;
+		return ((bytes - 1) >> 12) + 1;
 	}
 } // namespace memory