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/AzCore/Tests/StringFunc.cpp

@@ -966,7 +966,7 @@ namespace AZ
     {
     public:
         StringPathFuncTest() = default;
-        virtual ~StringPathFuncTest() = default;
+        ~StringPathFuncTest() override = default;
     };