There's no real reason this shouldn't be allowed, given some values sent
via a request can be signed. This also makes it less annoying to work
with popping enum values, given an enum class with no type specifier
will work out of the box now.

It's also kind of an oversight to allow popping s64 values, but nothing
else.

This is kind of a large hole in the API, given we allow popping signed
values. This fixes that.

Gets rid of a few unnecessary header dependencies in some source files.

Gets rid of the need to call the getter and then check for null.

As means to pave the way for getting rid of global state within core,
This eliminates kernel global state by removing all globals. Instead
this introduces a KernelCore class which acts as a kernel instance. This
instance lives in the System class, which keeps its lifetime contained
to the lifetime of the System class.

This also forces the kernel types to actually interact with the main
kernel instance itself instead of having transient kernel state placed
all over several translation units, keeping everything together. It also
has a nice consequence of making dependencies much more explicit.

This also makes our initialization a tad bit more correct. Previously we
were creating a kernel process before the actual kernel was initialized,
which doesn't really make much sense.

The KernelCore class itself follows the PImpl idiom, which allows
keeping all the implementation details sealed away from everything else,
which forces the use of the exposed API and allows us to avoid any
unnecessary inclusions within the main kernel header.

General moving to keep kernel object types separate from the direct
kernel code. Also essentially a preliminary cleanup before eliminating
global kernel state in the kernel code.

These aren't used externally at all, so they can be made private.

Allows pushing strongly-typed enum members without the need to always
cast them at the call sites.

Note that we *only* allow strongly-typed enums in this case. The reason
for this is that strongly typed enums have a guaranteed defined size, so
the size of the data being pushed is always deterministic. With regular
enums this can be a little more error-prone, so we disallow them.

This function simply uses the underlying type of the enum to determine
the size of the data. For example, if an enum is defined as:

enum class SomeEnum : u16 {
  SomeEntry
};

if PushEnum(SomeEnum::SomeEntry); is called, then it will push a
u16-size amount of data.

- This can be used for domain objects as inputs to service functions.

* Stub PopLaunchParameter and implement Buffer C Descriptors reading

* Address PR feedback

* Ensure we push a u64 not a size_t

* Fix formatting

They should have 32 bits of padding after the error code now.

Popping objects from the buffer is still not implemented.

IPC: Use the correct size when pushing raw data to the command buffer and fixed pushing domain objects.

Domain object ids are always stored immediately after the raw data.

Reduces the necessary allocation to max(in_handles, out_handles) rather
than (in_handles + out_handles).

These use the context functions to create and look-up handles for the
user.