Implement `logarithmic` flag for single slider widgets

[SamuMazzi]

Description: This PR implements logarithmic flag for the int/double/float_slider. This is done by refactoring a little bit the underlying structs.

I also removed vertical variable and used the flag ImGuiSliderFlags_Vertical, for coherence.

Also a little refactor regarding this PR has been done in mvBasicWidgets.cpp. pre_draw and post_draw parts were all the same (and sometimes with some typos) so I just wrapped them in two functions.

I think this are all changes to the codebase that are not essential, they are simple and I think they improve code quality, but I'd like a feedback on this.

Close #2404