tests: Add a test for struct constants going through typedefs.

tests/rust/const_generics_constant.rs

@@ -0,0 +1,18 @@
+#[repr(C)]
+pub struct FixedPoint<const FRACTION_BITS: u16> {
+    value: u16,
+}
+
+pub const FONT_WEIGHT_FRACTION_BITS: u16 = 6;
+
+pub type FontWeightFixedPoint = FixedPoint<FONT_WEIGHT_FRACTION_BITS>;
+
+#[repr(C)]
+pub struct FontWeight(FontWeightFixedPoint);
+
+impl FontWeight {
+    pub const NORMAL: FontWeight = FontWeight(FontWeightFixedPoint { value: 400 << FONT_WEIGHT_FRACTION_BITS });
+}
+
+#[no_mangle]
+pub extern "C" fn root(w: FontWeight) {}