[MLIR] Add f6E3M2FN type (#105573)

This PR adds `f6E3M2FN` type to mlir.

`f6E3M2FN` 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 S1E3M2. Unlike
IEEE-754 types, there are no infinity or NaN values.

```c
f6E3M2FN
- Exponent bias: 3
- Maximum stored exponent value: 7 (binary 111)
- Maximum unbiased exponent value: 7 - 3 = 4
- Minimum stored exponent value: 1 (binary 001)
- Minimum unbiased exponent value: 1 − 3 = −2
- Has Positive and Negative zero
- Doesn't have infinity
- Doesn't have NaNs

Additional details:
- Zeros (+/-): S.000.00
- Max normal number: S.111.11 = ±2^(4) x (1 + 0.75) = ±28
- Min normal number: S.001.00 = ±2^(-2) = ±0.25
- Max subnormal number: S.000.11 = ±2^(-2) x 0.75 = ±0.1875
- Min subnormal number: S.000.01 = ±2^(-2) x 0.25 = ±0.0625
```

Related PRs:
- [PR-94735](llvm/llvm-project#94735) [APFloat]
Add APFloat support for FP6 data types
- [PR-97118](llvm/llvm-project#97118) [MLIR] Add
f8E4M3 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 - Float6E3M2FNType.
+class PyFloat6E3M2FNType
+    : public PyConcreteType<PyFloat6E3M2FNType, PyFloatType> {
+public:
+  static constexpr IsAFunctionTy isaFunction = mlirTypeIsAFloat6E3M2FN;
+  static constexpr GetTypeIDFunctionTy getTypeIdFunction =
+      mlirFloat6E3M2FNTypeGetTypeID;
+  static constexpr const char *pyClassName = "Float6E3M2FNType";
+  using PyConcreteType::PyConcreteType;
+
+  static void bindDerived(ClassTy &c) {
+    c.def_static(
+        "get",
+        [](DefaultingPyMlirContext context) {
+          MlirType t = mlirFloat6E3M2FNTypeGet(context->get());
+          return PyFloat6E3M2FNType(context->getRef(), t);
+        },
+        py::arg("context") = py::none(), "Create a float6_e3m2fn type.");
+  }
+};
+
 /// Floating Point Type subclass - Float8E4M3FNType.
 class PyFloat8E4M3FNType
     : public PyConcreteType<PyFloat8E4M3FNType, PyFloatType> {
@@ -880,6 +901,7 @@ void mlir::python::populateIRTypes(py::module &m) {
   PyIntegerType::bind(m);
   PyFloatType::bind(m);
   PyIndexType::bind(m);
+  PyFloat6E3M2FNType::bind(m);
   PyFloat8E4M3FNType::bind(m);
   PyFloat8E5M2Type::bind(m);
   PyFloat8E4M3Type::bind(m);