`EvaluateExpression` does not always create a new persistent result. If the expression
is a bare persistent variable, then a new persistent result is not created. This means
the caller can't assume a new persistent result is created for each evaluation.
However, `dwim-print` was doing exactly that: assuming a new persistent result for each
evaluation. This resulted in a bug:
```
(lldb) p int $j = 23
(lldb) p $j
(lldb) p $j
```
The first `p $j` would not create a persistent result, and so `dwim-print` would
inadvertently delete `$j`. The second `p $j` would fail.
The fix is to try `expr` as a persistent variable, after trying `expr` as a frame
variable. For persistent variables, this avoids calling `EvaluateExpression`.
Resolves https://github.com/llvm/llvm-project/issues/84806
rdar://124688427
4da2b542b1