Add a test to check that all managed/unmanaged debug symbols are available

[omajid]

When we build .NET via source-build, it produces a .NET SDK that includes full debug symbols - both managed and unmanaged.

We should have a test that verifies that this debug information is actually present for all managed and unmanaged binaries to avoid discovering this post-release.

Here's an example where we were producing a binary that is missing debug information. dotnet/sdk-container-builds#440

See also: #2543

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