This PR introduces an implementation of the WAMR platform APIs for ESP-IDF and enables support for Espressif microcontrollers, and adds the documentation around how to build WAMR for ESP-IDF.
This PR is related to the following issues at WAMR: closes#883, #628, #449 and #668 as well as [#4735](https://github.com/espressif/esp-idf/issues/4735) at the esp-idf repo. It implements most functions required by [platform_api_vmcore.h](https://github.com/bytecodealliance/wasm-micro-runtime/blob/main/core/shared/platform/include/platform_api_vmcore.h).
The PR works in interpreter mode on Esp32c3 and Esp32. For the AOT mode, currently errors occur on both platforms with `Guru Meditation Error`. It seems that the AOT code isn't run with shared memory as os_mmap() allocates memory with malloc() API, it is to be fixed in the future.
