Enable operator<< for Half tensor (#3779)

Summary:
Pull Request resolved: #3779

Useful for debugging `Half` i.e. `fp16` models, when we have `EValue`s that are `Half` dtype and we do the following:
```
std::cout << "===== INPUT =====" << std::endl;
for (EValue& v : inputs) {
  std::cout << v << std::endl;
}

std::cout << "===== OUTPUT =====" << std::endl;
for (EValue& v : outputs) {
  std::cout << v << std::endl;
}
```

## Before
```
===== INPUT =====
tensor(sizes=[1, 3, 96, 72], [<unhandled scalar type 5>])
===== OUTPUT =====
tensor(sizes=[1, 2, 96, 72], [<unhandled scalar type 5>])
```

## After
```
===== INPUT =====
tensor(sizes=[1, 3, 96, 72], [0.279785, 0.271484, 0.364746, ..., 0.150391, 0.836426, 0.019043])
===== OUTPUT =====
tensor(sizes=[1, 2, 96, 72], [18.2344, -10.0938, 1.35059, ..., -33.6875, 4.07422, -22.5312])
```
ghstack-source-id: 228461839

Reviewed By: copyrightly

Differential Revision: D57977366

fbshipit-source-id: a9ba1c11f75af85dcf7c91b9b06b4ec3333455bc

Author: jorgep31415

extension/evalue_util/print_evalue.cpp

@@ -158,7 +158,7 @@ void print_tensor(std::ostream& os, exec_aten::Tensor tensor) {
     break;
 
   switch (tensor.scalar_type()) {
-    ET_FORALL_REAL_TYPES_AND(Bool, PRINT_TENSOR_DATA)
+    ET_FORALL_REAL_TYPES_AND2(Bool, Half, PRINT_TENSOR_DATA)
     default:
       os << "[<unhandled scalar type " << (int)tensor.scalar_type() << ">]";
   }