New unity component can be used for testing other applications.
Upstream version of Unity is included as a submodule.
Utilities specific to ESP-IDF unit tests (partitions, leak checking
setup/teardown functions, etc) are kept only in unit-test-app.
Kconfig options are added to allow disabling certain Unity features.
In earlier change this component was decoupled from freertos and hence
regression was introduced which changed default placement to flash. Some
device drivers make use of ringbuffer while flash cache is being disabled
and hence default placement should instead be internal memory.
Closes: https://github.com/espressif/esp-idf/issues/2517
