Merge pull request #23736 from seanm:c++11-simplifications

Removed all pre-C++11 code, workarounds, and branches #23736

This removes a bunch of pre-C++11 workrarounds that are no longer necessary as C++11 is now required.
It is a nice clean up and simplification.

* No longer unconditionally #include <array> in cvdef.h, include explicitly where needed
* Removed deprecated CV_NODISCARD, already unused in the codebase
* Removed some pre-C++11 workarounds, and simplified some backwards compat defines
* Removed CV_CXX_STD_ARRAY
* Removed CV_CXX_MOVE_SEMANTICS and CV_CXX_MOVE
* Removed all tests of CV_CXX11, now assume it's always true. This allowed removing a lot of dead code.
* Updated some documentation consequently.
* Removed all tests of CV_CXX11, now assume it's always true
* Fixed links.

---------

Co-authored-by: Maksim Shabunin <maksim.shabunin@gmail.com>
Co-authored-by: Alexander Smorkalov <alexander.smorkalov@xperience.ai>

modules/dnn/src/net_impl.cpp

@@ -918,7 +918,6 @@ AsyncArray Net::Impl::forwardAsync(const String& outputName)
     CV_Assert(!empty());
     FPDenormalsIgnoreHintScope fp_denormals_ignore_scope;
 
-#ifdef CV_CXX11
     String layerName = outputName;
 
     if (layerName.empty())
@@ -939,9 +938,6 @@ AsyncArray Net::Impl::forwardAsync(const String& outputName)
     isAsync = false;
 
     return getBlobAsync(layerName);
-#else
-    CV_Error(Error::StsNotImplemented, "DNN: Asynchronous forward requires build with enabled C++11");
-#endif  // CV_CXX11
 }