Modernization + AZStd::function compare fix. (#3680)

* Modernization + small fix.

Modernize ( `bool`/`override`/other) code in AzCore, AzFramework, AzQtComponents, AzToolsFramework, etc.
Replaced a `bind` or two, use `using` in a few places as well.

Fix nullptr comparison of AZStd::function.

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

* Apply review-based changes

Signed-off-by: nemerle <96597+nemerle@users.noreply.github.com>

Code/Framework/AzToolsFramework/Tests/EntityIdQLabelTests.cpp

@@ -55,7 +55,7 @@ namespace UnitTest
             AzToolsFramework::EditorRequests::Bus::Handler::BusConnect();
         }
 
-        ~EditorRequestHandlerTest()
+        ~EditorRequestHandlerTest() override
         {
             AzToolsFramework::EditorRequests::Bus::Handler::BusDisconnect();
         }