sirit: Add TypeSInt/TypeUInt helpers

Provides shorthands for specific signedness, so that usage code doesn't
need to explicitly use raw booleans.

TypeUInt(32), is easier to gloss than TypeInt(32, false), especially for
those not familiar with the API.

src/instructions/type.cpp

@@ -28,6 +28,14 @@ Id Module::TypeInt(int width, bool is_signed) {
     return *declarations << OpId{spv::Op::OpTypeInt} << width << is_signed << EndOp{};
 }
 
+Id Module::TypeSInt(int width) {
+    return TypeInt(width, true);
+}
+
+Id Module::TypeUInt(int width) {
+    return TypeInt(width, false);
+}
+
 Id Module::TypeFloat(int width) {
     declarations->Reserve(3);
     return *declarations << OpId{spv::Op::OpTypeFloat} << width << EndOp{};