Generate extension API shims

crates/libremetaverse-types/src/compat.rs

@@ -136,3 +136,15 @@ pub struct Span<T>(pub PhantomData<fn(T)>);
 pub struct RandomSource;
 
 pub struct IAsyncEnumerable<T>(pub PhantomData<fn() -> T>);
+
+pub struct ImmutableDictionary<TKey, TValue>(pub PhantomData<fn(TKey, TValue)>);
+
+pub struct ImmutableList<T>(pub PhantomData<fn(T)>);
+
+pub struct ICollection;
+
+pub struct UnicodeCategory(pub i32);
+
+pub struct TextEncoding;
+
+pub struct SocketException;