[llvm] [DirectX] Add `extract-section` to `llvm-objcopy` and implement it for `DXContainer` (PR #154804)

[Finn Plummer via llvm-commits]

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+## Tests that a separate DXContainer is created for the RTS0 (root signature)
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inbelic wrote:

Renamed the files.
I did note that other similar testing had a case for single vs many option(s) specified, so they are left as-is for now. But happy to condense them

https://github.com/llvm/llvm-project/pull/154804