Add symbol value origin tracking

Track the origin of configuration symbol values through a new 'origin'
property. This allows users to understand how and where each symbol's
value was determined.

Features:
- Track 5 kinds of value origins: assign, default, select, imply, unset
- Record location information (filename, line number) for value sources
- Refactor MenuNode to use 'loc' tuple instead of separate
  filename/linenr
- Maintain backward compatibility with filename/linenr properties
- Extend set_value() API with optional 'loc' parameter

The implementation provides detailed insight into configuration symbol
derivation, which is valuable for debugging complex Kconfig scenarios.

Based on zephyrproject-rtos/Kconfiglib#18 by Luca Burelli.

Signed-off-by: Jim Huang <[email protected]>

Author: pillo79