Reduction of the number of constructors for raylib::Rectangle

[Bigfoot71]

I reduced the number of constructors for raylib::Rectangle using default parameters.

[RobLoach]

Thanks. I forget why I opted to manually implement these. I think there was an issue with one version of C++ that had conflict between the default parameters and initializer lists. That could no longer be a problem though 🤔

[Bigfoot71]

I personally have no problem compiling it with GCC 11.4.0, whether it's with -std=c++11 or -std=c++17. I could perform more thorough tests when I have the time, if you'd like.

[kyomawolf]

Whats up with this PR? Do you know why the build fails?

[RobLoach]

If we do take this approach, I'd like to do a few things...

• Add more tests to make sure the constructors still work properly
• Apply the same pattern across the rest of the data types

I do remember running into an issue with the initializer list understanding the default parameters, but I'm not sure where/when it happened.