[LLDB] Process minidump better error messages (#149206)
Prior, Process Minidump would return
```
Status::FromErrorString("could not parse memory info");
```
For any unsuccessful memory read, with no differentiation between an
error in LLDB and the data simply not being present. This lead to a lot
of user confusion and overall pretty terrible user experience. To fix
this I've refactored the APIs so we can pass an error back in an llvm
expected.
There were also no shell tests for memory read and process Minidump so I
added one.
