[MLIR] Add f6E2M3FN type (#107999)

This PR adds `f6E2M3FN` type to mlir.

`f6E2M3FN` type is proposed in [OpenCompute MX
Specification](https://www.opencompute.org/documents/ocp-microscaling-formats-mx-v1-0-spec-final-pdf).
It defines a 6-bit floating point number with bit layout S1E2M3. Unlike
IEEE-754 types, there are no infinity or NaN values.

```c
f6E2M3FN
- Exponent bias: 1
- Maximum stored exponent value: 3 (binary 11)
- Maximum unbiased exponent value: 3 - 1 = 2
- Minimum stored exponent value: 1 (binary 01)
- Minimum unbiased exponent value: 1 − 1 = 0
- Has Positive and Negative zero
- Doesn't have infinity
- Doesn't have NaNs

Additional details:
- Zeros (+/-): S.00.000
- Max normal number: S.11.111 = ±2^(2) x (1 + 0.875) = ±7.5
- Min normal number: S.01.000 = ±2^(0) = ±1.0
- Max subnormal number: S.00.111 = ±2^(0) x 0.875 = ±0.875
- Min subnormal number: S.00.001 = ±2^(0) x 0.125 = ±0.125
```

Related PRs:
- [PR-94735](llvm/llvm-project#94735) [APFloat]
Add APFloat support for FP6 data types
- [PR-105573](llvm/llvm-project#105573) [MLIR]
Add f6E3M2FN type - was used as a template for this PR

Author: sergey-kozub

IRTypes.cpp

@@ -124,6 +124,27 @@ class PyFloatType : public PyConcreteType<PyFloatType> {
   }
 };
 
+/// Floating Point Type subclass - Float6E2M3FNType.
+class PyFloat6E2M3FNType
+    : public PyConcreteType<PyFloat6E2M3FNType, PyFloatType> {
+public:
+  static constexpr IsAFunctionTy isaFunction = mlirTypeIsAFloat6E2M3FN;
+  static constexpr GetTypeIDFunctionTy getTypeIdFunction =
+      mlirFloat6E2M3FNTypeGetTypeID;
+  static constexpr const char *pyClassName = "Float6E2M3FNType";
+  using PyConcreteType::PyConcreteType;
+
+  static void bindDerived(ClassTy &c) {
+    c.def_static(
+        "get",
+        [](DefaultingPyMlirContext context) {
+          MlirType t = mlirFloat6E2M3FNTypeGet(context->get());
+          return PyFloat6E2M3FNType(context->getRef(), t);
+        },
+        py::arg("context") = py::none(), "Create a float6_e2m3fn type.");
+  }
+};
+
 /// Floating Point Type subclass - Float6E3M2FNType.
 class PyFloat6E3M2FNType
     : public PyConcreteType<PyFloat6E3M2FNType, PyFloatType> {
@@ -901,6 +922,7 @@ void mlir::python::populateIRTypes(py::module &m) {
   PyIntegerType::bind(m);
   PyFloatType::bind(m);
   PyIndexType::bind(m);
+  PyFloat6E2M3FNType::bind(m);
   PyFloat6E3M2FNType::bind(m);
   PyFloat8E4M3FNType::bind(m);
   PyFloat8E5M2Type::bind(m);