Convert small PyQt script to Qt C++

[J.Hilk]

@Kris-Revi
Merry Christmas!

https://github.com/DeiVadder/QWidgetGradient.git

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After some testing, the functionality is kind of strange, not sure if thats intended behavior, or if I made a bug 🤔
For you to find out I guess 😜

[Kris Revi]

@J-Hilk wow, thank you sooo much! christmas came early!! <3

i get these errors in the Header file alone

G:\QT GUI\TesterGradient\gradient.h:31: error: C2429: attribute 'nodiscard' requires compiler flag '/std:c++17'
G:\QT GUI\TesterGradient\gradient.cpp:3: error: C2653: 'gradient': is not a class or namespace name
G:\QT GUI\TesterGradient\gradient.cpp:4: error: C4430: missing type specifier - int assumed. Note: C++ does not support default-int
G:\QT GUI\TesterGradient\gradient.cpp:6: warning: C4508: 'gradient': function should return a value; 'void' return type assumed
g:\qt gui\build-testergradient-desktop_qt_5_15_1_msvc2019_32bit-debug\debug\..\..\TesterGradient\gradient.h:31: error: C2429: attribute 'nodiscard' requires compiler flag '/std:c++17'

[J.Hilk]

@Kris-Revi well, it compiles for me :P

remove the [[nodiscard]] attribute, its not needed, and if your compiler is not c++17 capable, no need to have it there

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Edit: check the repo, I updated it, inclusive a bugfix I found.