runtime(termdebug): Refactored StartDebug_term and EndDebug functions

runtime(termdebug): Refactored StartDebug_term and EndDebug functions

- Functions are way too long. Readability and maintainability should
be slightly improved.

- Some variables are re-assigned to their initial value at teardown.
This should not be needed since all internal variables are
re-initialized at startup of every Termdebug session.

closes: #15086

Signed-off-by: Ubaldo Tiberi <ubaldo.tiberi@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>