Fix ambiguous text of GetCopyableFootprints function

[alpakaDurumi]

The current explanation for BaseOffset parameter is ambiguous. It is described as The offset, in bytes, to the resource., which can be incorrectly interpreted as an offset of the resource represented by the pResourceDesc parameter.

In the function, BaseOffset is not an offset for the resource. Instead, it is a value that is simply added to the Offset of each subresource layout in the output pLayouts array.

For reference, see d3dx12.h version of GetCopyableFootprints : https://github.com/microsoft/DirectX-Headers/blob/18d5bfe96452667b201fd26aa25c6c305ae57e07/include/directx/d3dx12_resource_helpers.h#L520

[alpakaDurumi]

@microsoft-github-policy-service agree

[prmerger-automator]

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