* Changed project AVR_Dx_IAR to use 'heap_1.c'.
* AVR_Dx_IAR project cleanup.
* AVR_ATMega4809_IAR project cleanup.
* Added newline at end of .gitignore file for AVR_Dx_IAR and AVR_ATMega0_IAR projects.
* Updated indentation in AVR_ATMega4809_Atmel_Studio and AVR_Dx_Atmel_Studio projects, plus small fixes in their readme files.
* Added AVR_ATMega4809_IAR, AVR_ATMega4809_MPLAB.X, AVR_Dx_IAR and AVR_Dx_MPLAB.X demo projects.
* Removed build artefacts and added .gitignore files in AVR_ATMega4809_MPLAB.X and AVR_Dx_MPLAB.X projects.
Co-authored-by: Yuhui Zheng <10982575+yuhui-zheng@users.noreply.github.com>