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>

---------

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/dotnet/Context.cs

@@ -474,6 +474,36 @@ namespace Microsoft.Z3
             return new DatatypeSort(this, symbol, constructors);
         }
 
+        /// <summary>
+        /// Create a forward reference to a datatype sort.
+        /// This is useful for creating recursive datatypes or parametric datatypes.
+        /// </summary>
+        /// <param name="name">name of the datatype sort</param>
+        /// <param name="parameters">optional array of sort parameters for parametric datatypes</param>
+        public DatatypeSort MkDatatypeSortRef(Symbol name, Sort[] parameters = null)
+        {
+            Debug.Assert(name != null);
+            CheckContextMatch(name);
+            if (parameters != null)
+                CheckContextMatch<Sort>(parameters);
+            
+            var numParams = (parameters == null) ? 0 : (uint)parameters.Length;
+            var paramsNative = (parameters == null) ? null : AST.ArrayToNative(parameters);
+            return new DatatypeSort(this, Native.Z3_mk_datatype_sort(nCtx, name.NativeObject, numParams, paramsNative));
+        }
+
+        /// <summary>
+        /// Create a forward reference to a datatype sort.
+        /// This is useful for creating recursive datatypes or parametric datatypes.
+        /// </summary>
+        /// <param name="name">name of the datatype sort</param>
+        /// <param name="parameters">optional array of sort parameters for parametric datatypes</param>
+        public DatatypeSort MkDatatypeSortRef(string name, Sort[] parameters = null)
+        {
+            using var symbol = MkSymbol(name);
+            return MkDatatypeSortRef(symbol, parameters);
+        }
+
         /// <summary>
         /// Create mutually recursive datatypes.
         /// </summary>