Windows compatibility, Qt 6 compatibility

[u-an-i]

Windows compatibility:

• Windows does not support "mkdir" to fail silently, a prepiped rmdir would work but neither the copy nor the echo ("Write-Information") command work by pipe as required thus the command gets deleted overall and the folder replaced by a symlink
• Windows OpenGL does not like Qt OpenGL calls without "context"

Qt 6 compatibility:

• Qt 3D has 2 changes which are now catered for

Qt project file:

• quoted paths to support whitespace in path names
• made disjunct parts faster recognizable (hopefully)

Notes:

• the Qt 5 lib folder files are 32-bit, the Qt 6 lib-qt6 folder files are 64-bit; only new binaries pushed, the present .a which the build created anew was not
• the test exe when launched errors about not having some Qt dlls inside its working folder but when they are present the exe errors with "no Qt platform plugin could be initialized"