[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/base/testing/threading_test.cc

@@ -824,7 +824,7 @@ TEST_CASE("Create and Run Thread", "[thread]") {
   }
 
   SECTION("16kb stack size") {
-    params.stack_size = 16 * 1024 * 1024;
+    params.stack_size = 16_MiB;
     thread = Thread::Create(params, [] {
       Thread::Exit(-1);
       FAIL("Function must not return");