rustdoc-search: fix bugs when unboxing and reordering combine

tests/rustdoc-js/generics-unbox.rs

@@ -0,0 +1,36 @@
+pub struct Out<A, B = ()> {
+    a: A,
+    b: B,
+}
+
+pub struct Out1<A, const N: usize> {
+    a: [A; N],
+}
+
+pub struct Out2<A, const N: usize> {
+    a: [A; N],
+}
+
+pub struct Out3<A, B> {
+    a: A,
+    b: B,
+}
+
+pub struct Out4<A, B> {
+    a: A,
+    b: B,
+}
+
+pub struct Inside<T>(T);
+
+pub fn alpha<const N: usize, T>(_: Inside<T>) -> Out<Out1<T, N>, Out2<T, N>> {
+    loop {}
+}
+
+pub fn beta<T, U>(_: Inside<T>) -> Out<Out3<T, U>, Out4<U, T>> {
+    loop {}
+}
+
+pub fn gamma<T, U>(_: Inside<T>) -> Out<Out3<U, T>, Out4<T, U>> {
+    loop {}
+}