Hashing for constant and singleton SymInt/SymBool (#109170)

Bugfix:
- previously, SymBool does not implement `__eq__`, Python falls back to default `__eq__ `and `__hash__`
- in this PR, we make SymBool implement `__eq__`
- symbolic SymBool now raises an error when hashed just like SymInt/SymFloat

New feature:
- previously, SymInt and SymFloat are unhashable (even if you are singleton or constant)
- in this PR, SymInt and SymBool are hashable if singleton/constant

Stay the same:
- SymNode are hashable due to default Python behavior
Pull Request resolved: https://github.com/pytorch/pytorch/pull/109170
Approved by: https://github.com/ezyang
ghstack dependencies: #109169

torch/csrc/jit/python/init.cpp

@@ -1265,6 +1265,11 @@ void initJITBindings(PyObject* module) {
           "is_symbolic",
           [](const c10::SymNode& node) {
             return node->is_symbolic();
+          })
+      .def(
+          "singleton_int",
+          [](const c10::SymNode& node) {
+            return node->singleton_int();
           });
 
   // clang-format on