[Base] Add user-literals for several memory sizes

Rather than using `n * 1024 * 1024`, this adds a convenient `_MiB`/`_KiB` user-literal to the new `literals.h` header to concisely describe units of memory in a much more readable way. Any other useful literals can be added to this header. These literals exist in the `xe::literals` namespace so they are opt-in, similar to `std::chrono` literals, and require a `using namespace xe::literals` statement to utilize it within the current scope.

I've done a pass through the codebase to replace trivial instances of `1024 * 1024 * ...` expressions being used but avoided anything that added additional casting complexity from `size_t` to `uint32_t` and such to keep this commit concise.

src/xenia/gpu/d3d12/deferred_command_list.h

@@ -16,6 +16,7 @@
 #include <vector>
 
 #include "xenia/base/assert.h"
+#include "xenia/base/literals.h"
 #include "xenia/base/math.h"
 #include "xenia/ui/d3d12/d3d12_api.h"
 
@@ -23,12 +24,14 @@ namespace xe {
 namespace gpu {
 namespace d3d12 {
 
+using namespace xe::literals;
+
 class D3D12CommandProcessor;
 
 class DeferredCommandList {
  public:
   DeferredCommandList(const D3D12CommandProcessor& command_processor,
-                      size_t initial_size_bytes = 1024 * 1024);
+                      size_t initial_size_bytes = 1_MiB);
 
   void Reset();
   void Execute(ID3D12GraphicsCommandList* command_list,