MC's Tab in hex mode toggles the cursor between the hex data area
and the ASCII text column (hexview_in_text). Add this feature:
- Viewer::hexview_in_text: bool field (default false)
- Tab key in Hex/HexEdit mode toggles the flag
- ViewerCmd::ToggleHexNavigation + View menu entry in F9
- execute_menubar_cmd dispatches the toggle
The hex render uses hexview_in_text to determine which column
gets the cursor highlight (hex bytes vs ASCII representation).
Tests: 1420 pass, zero warnings.
vasilito
a99fb17568