Add FAQ entry for x64 shell extension DLL on Arm64

[cts-davean]

64-bit shell extension DLLs installed on Arm64 devices should be built for Arm64X to support loading in both Arm64 and x64 processes.

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Issue	Description
Yaml File(s)	This PR includes changes to .yml file(s) owned by another author.

[mattwojo]

Thanks for contributing this @cts-davean. I shared with the dev team and they said that we should add a bit of additional context about how shell extensions work (in-process vs out-of-process). I'm going to follow up to see if we can capture some of that nuance in a concise way to include in this FAQ before we merge it in.