[lldb][lldb-dap] use the new protocol for setVariable requests. (#137803)

```cpp

// The "id" is the unique integer ID that is unique within the enclosing
// variablesReference. It is optionally added to any "interface
Variable"
  // objects to uniquely identify a variable within an enclosing
// variablesReference. It helps to disambiguate between two variables
that
// have the same name within the same scope since the "setVariables"
request
// only specifies the variable reference of the enclosing
scope/variable, and
// the name of the variable. We could have two shadowed variables with
the
// same name in "Locals" or "Globals". In our case the "id" absolute
index
  // of the variable within the dap.variables list.
  const auto id_value =
      GetInteger<uint64_t>(arguments, "id").value_or(UINT64_MAX);
  if (id_value != UINT64_MAX) {
```
I dropped this part because. variables that have the same name has a ` @path` suffix on both of them. 
and the setVariableArguments does not have a field called `id`.