Add first-class support to create dump files from the debugger

[xusheng6]

Right now the user can create a dump file via a backend command: https://github.com/Vector35/debugger/issues/647. However, this is not convenient and not very discoverable. We should improved it in two possible ways:

1. Add a new capacity for the backend to create a dump file. Basically the adapter will be responsible for creating the dump file, and the DbgEng/LLDB adapter will be responsible for doing that. We can have a UI/API to make the feature more accessible
2. Add a way to save the current state of the target as a binja database. Memory regions are saved as segments, and register values, thread states, etc, are saved as metadata

[xusheng6]

Over the long run we can also try adding the support to fix and dump the file after unpacking as detailed in https://github.com/Vector35/debugger/issues/471