This commit refactors the FreeRTOS documentation as follows:
- Rewrite FreeRTOS SMP changes document (ESP-IDF FreeRTOS SMP)
- Reorganized sections in kernel behavior changes
- Rewrote descriptions of each kernel behavior changes
- Added notes about using ESP-IDF FreeRTOS for single core targets
- Moved TLSP callback section to FreeRTOS Additions document
- Moved FreeRTOS configuration section to FreeRTOS API document
- Added notes about FreeRTOS applications in ESP-IDF