Add DeviceAllocator as the base device allocator (#138222)

# Motivation
In line with [RFC] [A device-agnostic Python device memory related API design for stream-based accelerators](https://github.com/pytorch/pytorch/issues/134978), some memory-related APIs are widely used in popular repositories, such as HuggingFace [so many if-else conditional code](https://github.com/search?q=repo%3Ahuggingface%2Faccelerate%20torch.cuda.empty_cache&type=code). We would like to introduce a generic API set under torch.accelerator namespace to generalize these user cases.

<div align="center">
<table>
<tr>
<td> Device-specific memory APIs torch.xxx.foo</td> <td> Device-agnostic memory APIs torch.accelerator.foo</td>
</tr>
<tr>
<td>

```python
torch.xxx.empty_cache
```

</td>
<td>

```python
torch.accelerator.empty_cache
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.reset_peak_memory_stats
```

</td>
<td>

```python
torch.accelerator.reset_peak_memory_stats
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.reset_accumulated_memory_stats
```

</td>
<td>

```python
torch.accelerator.reset_accumulated_memory_stats
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.memory_stats
```

</td>
<td>

```python
torch.accelerator.memory_stats
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.memory_allocated
```

</td>
<td>

```python
torch.accelerator.memory_allocated
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.max_memory_allocated
```

</td>
<td>

```python
torch.accelerator.max_memory_allocated
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.memory_reserved
```

</td>
<td>

```python
torch.accelerator.memory_reserved
```

</td>
</tr>

<tr>
<td>

```python
torch.xxx.max_memory_reserved
```

</td>
<td>

```python
torch.accelerator.max_memory_reserved
```

</td>
</tr>

</table>
</div>

# Solution
This design follows a similar pattern to `HostAllocator`. We're introducing a base class `DeviceAllocator`, from which `CUDAAllocator` and `XPUAllocator` will inherit. This allows us to provide a unified call path like: `torch.accelerator.empty_cache()` -> `GetDeviceAllocator(allocator)->empty_cache()`.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/138222
Approved by: https://github.com/albanD, https://github.com/Camyll

c10/xpu/XPUCachingAllocator.cpp

@@ -540,7 +540,7 @@ class DeviceCachingAllocator {
 
 static void local_raw_delete(void* ptr);
 
-class XPUAllocator : public Allocator {
+class XPUAllocator : public DeviceAllocator {
  private:
   std::mutex mutex;
   ska::flat_hash_map<void*, Block*> allocated_blocks;
@@ -576,6 +576,10 @@ class XPUAllocator : public Allocator {
     }
   }
 
+  bool initialized() override {
+    return !device_allocators.empty();
+  }
+
   void malloc(
       void** devPtr,
       DeviceIndex device,
@@ -610,13 +614,13 @@ class XPUAllocator : public Allocator {
     }
   }
 
-  void emptyCache() {
+  void emptyCache(MempoolId_t mempool_id [[maybe_unused]] = {0, 0}) override {
     for (auto& da : device_allocators) {
       da->emptyCache();
     }
   }
 
-  void recordStream(const DataPtr& ptr, XPUStream stream) {
+  void recordStream(const DataPtr& ptr, c10::Stream stream) override {
     if (!ptr.get()) {
       return;
     }
@@ -626,7 +630,8 @@ class XPUAllocator : public Allocator {
 
     Block* block = get_allocated_block(ptr.get());
     TORCH_CHECK(block, "No allocated block can be found.");
-    device_allocators[block->device]->recordStream(block, stream);
+    c10::xpu::XPUStream xpu_stream{stream};
+    device_allocators[block->device]->recordStream(block, xpu_stream);
   }
 
   DataPtr allocate(size_t size) override {
@@ -679,17 +684,17 @@ class XPUAllocator : public Allocator {
         ": did you call init?");
   }
 
-  DeviceStats getDeviceStats(DeviceIndex device) {
+  DeviceStats getDeviceStats(DeviceIndex device) override {
     assertValidDevice(device);
     return device_allocators[device]->getStats();
   }
 
-  void resetPeakStats(DeviceIndex device) {
+  void resetPeakStats(DeviceIndex device) override {
     assertValidDevice(device);
     device_allocators[device]->resetPeakStats();
   }
 
-  void resetAccumulatedStats(DeviceIndex device) {
+  void resetAccumulatedStats(DeviceIndex device) override {
     assertValidDevice(device);
     device_allocators[device]->resetAccumulatedStats();
   }