Previously, the debugger displayed `ref int` variables like this:
ref_int: <unsupported-data-type>
<void>: <unsupported-data-type>
This commit introduces `dbg_variable_to_string()` to dereference these
variables and display their underlying value. Both the command-line and
DAP debugger interfaces have been updated to use this new functionality.
kichikuou
729957b842