[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/emulator.cc

@@ -20,6 +20,7 @@
 #include "xenia/base/cvar.h"
 #include "xenia/base/debugging.h"
 #include "xenia/base/exception_handler.h"
+#include "xenia/base/literals.h"
 #include "xenia/base/logging.h"
 #include "xenia/base/mapped_memory.h"
 #include "xenia/base/profiling.h"
@@ -60,6 +61,8 @@ DEFINE_string(
 
 namespace xe {
 
+using namespace xe::literals;
+
 Emulator::Emulator(const std::filesystem::path& command_line,
                    const std::filesystem::path& storage_root,
                    const std::filesystem::path& content_root,
@@ -415,8 +418,7 @@ bool Emulator::SaveToFile(const std::filesystem::path& path) {
   Pause();
 
   filesystem::CreateFile(path);
-  auto map = MappedMemory::Open(path, MappedMemory::Mode::kReadWrite, 0,
-                                1024ull * 1024ull * 1024ull * 2ull);
+  auto map = MappedMemory::Open(path, MappedMemory::Mode::kReadWrite, 0, 2_GiB);
   if (!map) {
     return false;
   }