Technical Debt: Std Library and Linux

[greenfire27]

Some standard library containers do not work on Linux platform (ex, std:unordered_map)

[elementc]

I observed this while writing #43 which is a fix for #42.

On 43, we fixed the following compilation error which occurred when 128750d added a std::unordered_map to GuiControlProfile:

make: *** [Torque2D.mk:130: Debug/2d/controllers/core/PickingSceneController.cc.o] Error 1
In file included from /usr/include/c++/9/unordered_map:47,
                 from ../../source/gui/guiTypes.h:63,
                 from ../../source/gui/guiControl.h:42,
                 from ../../source/2d/core/ImageFrameProviderCore.h:51,
                 from ../../source/2d/core/ImageFrameProvider.h:27,
                 from ../../source/2d/core/SpriteBatchItem.h:27,
                 from ../../source/2d/core/SpriteBatch.h:27,
                 from ../../source/2d/core/SpriteBatchQuery.cc:26:
/usr/include/c++/9/bits/unordered_map.h:40:37: error: '_Hashtable_traits' in namespace 'std::__detail' does not name a template type

On #43 we papered over the issue by replacing the offending std::unordered_map with the Torque-internal HashMap which is a drop-in replacement. However, it's silly to not be able to use perfectly good container types from the standard library, and likely will drive off users who will want to be able to use the C++ constructs they know and love.

On this ticket, we should definitely investigate and fix this issue.

Would-be investigators will note that, following #31, the Makefile-backed Linux build on the development branch has been slightly overhauled, including building in a Docker container that provides somewhat-tighter controls of our toolchain. In this case, the Dockerfile in engine/compilers/Make-{32,64}bit/ pins an Ubuntu 20.04 build environment, and uses the distro-default build-essential packages.
This loosely pins us to the following build of GCC:

casey on WATERFALCON in ~ 
at 09:02:55 🍀 docker run -it torque2d-linux64-build-env
root@5998068a57ba:/# g++ --version
g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
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