Prior to this patch, each core file plugin (ObjectFileMachO.cpp and
ObjectFileMinindump.cpp) would calculate the address ranges to save in
different ways. This patch adds a new function to Process.h/.cpp:
```
Status Process::CalculateCoreFileSaveRanges(lldb::SaveCoreStyle core_style, CoreFileMemoryRanges &ranges);
```
The patch updates the ObjectFileMachO::SaveCore(...) and
ObjectFileMinindump::SaveCore(...) to use same code. This will allow
core files to be consistent with the lldb::SaveCoreStyle across
different core file creators and will allow us to add new core file
saving features that do more complex things in future patches.
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