check the usage of expstring_t in the runtime (core)

Submitted by Kristof Szabados

Description

expstring_t is a special type (actually typedef) used in the compiler, to help with generating large amounts of code, and also provide us with debugging support.

It should not have been used in the generated code and the runtime executables. But for some reason it has sneaked into the core folder, and is used in logging.

This should be reviewed, and if possible replaced with char* to be in line with the original plans. Also as the necessary tools providing the benefit of this type in the compiler are not available in the runtime ... there is no purpose of this type there.

Version: 7.1.0