Replace usage of std::is_pod (#7303)

Replaces usages of `std::is_pod` with the suggested alternative by gcc -
`std::is_standard_layout && std::is_trivial`. `std::is_pod` is
deprecated in C++20, hence this replacement is necessary to make usage
of open3d possible when client code is compiled with C++20.

Fixes part of #5405

Author: vawale

CHANGELOG.md

@@ -62,6 +62,7 @@
 -   Add error handling for insufficient correspondences in AdvancedMatching (PR #7234)
 -   Exposed `get_plotly_fig` and modified `draw_plotly` to return the `Figure` it creates. (PR #7258)
 -   Fix build with librealsense v2.44.0 and upcoming VS 2022 17.13 (PR #7074)
+-   Fix `deprecated-declarations` warnings when compiling code with C++20 standard (PR #7303)
 
 ## 0.13
 

cpp/open3d/core/Tensor.h

@@ -62,8 +62,9 @@ class Tensor : public IsDevice {
 
         // Check data types
         AssertTemplateDtype<T>();
-        if (!std::is_pod<T>()) {
-            utility::LogError("Object must be a POD.");
+        if (!(std::is_standard_layout<T>::value && std::is_trivial<T>::value)) {
+            utility::LogError(
+                    "Object must be a StandardLayout and TrivialType type.");
         }
 
         // Copy data to blob
@@ -1432,4 +1433,4 @@ inline void AssertNotSYCL(const Tensor& tensor) {
 }
 
 }  // namespace core
-}  // namespace open3d
+}  // namespace open3d

cpp/open3d/ml/contrib/Cloud.cpp

@@ -53,7 +53,9 @@ namespace open3d {
 namespace ml {
 namespace contrib {
 
-static_assert(std::is_pod<PointXYZ>(), "PointXYZ class must be a POD type.");
+static_assert(std::is_standard_layout<PointXYZ>::value &&
+                      std::is_trivial<PointXYZ>::value,
+              "PointXYZ class must be a StandardLayout and TrivialType type.");
 
 // Getters
 // *******

cpp/tests/core/TensorObject.cpp

@@ -48,7 +48,9 @@ class TestObject {
     void *ptr_;
 };
 
-static_assert(std::is_pod<TestObject>(), "TestObject must be a POD.");
+static_assert(std::is_standard_layout<TestObject>::value &&
+                      std::is_trivial<TestObject>::value,
+              "TestObject must be a StandardLayout and TrivialType type.");
 static const int64_t byte_size = sizeof(TestObject);
 static const std::string class_name = "TestObject";