Add break for default cases

Visual Studio has an option to search all files in a solution, so I
did a search in there for "default:" looking for any missing break
statements.

I've left out default statements that return something, and that throw
something, even if via ThrowInvalidType. UNREACHABLE leads towards throw

R_THROW macro leads towards a return

src/core/hle/kernel/init/init_slab_setup.cpp

@@ -243,6 +243,7 @@ void InitializeSlabHeaps(Core::System& system, KMemoryLayout& memory_layout) {
             // If we somehow get an invalid type, abort.
         default:
             ASSERT_MSG(false, "Unknown slab type: {}", slab_types[i]);
+            break;
         }
 
         // If we've hit the end of a gap, free it.