[lldb] [llvm] [lldb-dap] Add multi-session support with shared debugger instances (PR #163653)

[John Harrison via llvm-commits]

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ashgti wrote:

Small nit, but we could just call this `SessionManager`, its already in the lldb_dap namespace. But not that big of a deal either way.

https://github.com/llvm/llvm-project/pull/163653