Update Z3_mk_datatype_sort API to accept array of sort parameters and add Z3_mk_polymorphic_datatype (#7966)

* Initial plan

* Update Z3_mk_datatype_sort API to accept array of parameters

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Update language bindings for parametric datatype sort API

- Python: Updated DatatypeSort() to accept optional params list
- OCaml: Added mk_sort_ref_p/mk_sort_ref_ps for parametric datatypes
- .NET: Added MkDatatypeSortRef() methods with optional params
- Java: Added mkDatatypeSortRef() methods with optional params
- All changes maintain backward compatibility

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Fix .NET build error - rename params to parameters

The 'params' keyword is reserved in C#, causing compilation errors.
Renamed parameter from 'params' to 'parameters' in MkDatatypeSortRef methods.

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Add unit test for parametric datatypes

Added test_parametric_datatype.cpp to demonstrate polymorphic datatypes.
The test creates two concrete instantiations of a generic pair concept:
- pair_int_real with fields (first:Int, second:Real)
- pair_real_int with fields (first:Real, second:Int)
Then verifies that accessors work correctly and type checking is enforced.

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Implement polymorphic type variables support for parametric datatypes

- Modified datatype_decl_plugin to allow type variables as parameters
- Updated mk_datatype_decl to extract type variables from field sorts
- Type variables are collected in order of first appearance
- Revised unit test to use Z3_mk_type_variable for polymorphic datatypes
- Test creates pair datatype with type variables alpha and beta
- Successfully instantiates with concrete types (pair Int Real) and (pair Real Int)
- Verifies accessor types match and equality terms are well-typed
- All tests pass

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Add Z3_mk_polymorphic_datatype API and refactor datatype creation

- Added new API Z3_mk_polymorphic_datatype to z3_api.h
- Renamed static mk_datatype_decl to api_datatype_decl in api_datatype.cpp
- Modified api_datatype_decl to accept explicit type parameters
- Updated all callers to use renamed function
- Added test_polymorphic_datatype_api demonstrating new API usage
- Both tests pass successfully

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Remove type variable collection logic from constructors

Removed the logic for collecting type variables from field sorts based on constructors.

* Update comments on parameter handling in api_datatype.cpp

Clarify usage of parameters in API documentation.

* Fix OCaml build error - use list instead of array for mk_datatype_sort

Changed mk_sort_ref to pass empty list [] instead of empty array [||].
Changed mk_sort_ref_p to pass params list directly instead of converting to array.
Z3native.mk_datatype_sort expects a list, not an array.

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

* Add polymorphic datatype example to C++ examples

Added polymorphic_datatype_example() demonstrating:
- Creating type variables alpha and beta with Z3_mk_type_variable
- Defining parametric Pair datatype with fields of type alpha and beta
- Instantiating with concrete types (Pair Int Real) and (Pair Real Int)
- Getting constructors and accessors from instantiated datatypes
- Creating constants and expressions using the polymorphic types
- Verifying type correctness with equality (= (first p1) (second p2))

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>
Co-authored-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/java/Context.java

@@ -388,6 +388,54 @@ public class Context implements AutoCloseable {
         return new DatatypeSort<>(this, mkSymbol(name), constructors);
     }
 
+    /**
+     * Create a forward reference to a datatype sort.
+     * This is useful for creating recursive datatypes or parametric datatypes.
+     * @param name name of the datatype sort
+     * @param params optional array of sort parameters for parametric datatypes
+     **/
+    public <R> DatatypeSort<R> mkDatatypeSortRef(Symbol name, Sort[] params)
+    {
+        checkContextMatch(name);
+        if (params != null)
+            checkContextMatch(params);
+        
+        int numParams = (params == null) ? 0 : params.length;
+        long[] paramsNative = (params == null) ? new long[0] : AST.arrayToNative(params);
+        return new DatatypeSort<>(this, Native.mkDatatypeSort(nCtx(), name.getNativeObject(), numParams, paramsNative));
+    }
+
+    /**
+     * Create a forward reference to a datatype sort (non-parametric).
+     * This is useful for creating recursive datatypes.
+     * @param name name of the datatype sort
+     **/
+    public <R> DatatypeSort<R> mkDatatypeSortRef(Symbol name)
+    {
+        return mkDatatypeSortRef(name, null);
+    }
+
+    /**
+     * Create a forward reference to a datatype sort.
+     * This is useful for creating recursive datatypes or parametric datatypes.
+     * @param name name of the datatype sort
+     * @param params optional array of sort parameters for parametric datatypes
+     **/
+    public <R> DatatypeSort<R> mkDatatypeSortRef(String name, Sort[] params)
+    {
+        return mkDatatypeSortRef(mkSymbol(name), params);
+    }
+
+    /**
+     * Create a forward reference to a datatype sort (non-parametric).
+     * This is useful for creating recursive datatypes.
+     * @param name name of the datatype sort
+     **/
+    public <R> DatatypeSort<R> mkDatatypeSortRef(String name)
+    {
+        return mkDatatypeSortRef(name, null);
+    }
+
     /**
      * Create mutually recursive datatypes. 
      * @param names names of datatype sorts