Refactor run_microdroid_demo.sh for clarity and modularity

- Extracted TC Microdroid demo app commands into handle_run_tc_app_cmd function
- Added ADB and directory variable definitions for reuse
- Used case statement to handle 'run-tc-app' command and future commands
- Removed redundant inline commands and improved readability

Signed-off-by: Ahmed Genidi <ahmed.genidi@arm.com>