CPUSets for game development: Fix code snippets

[CookiePLMonster]

This PR fixes multiple issues with code snippets on the CPUSets for game development page:

1. An example usage of SetThreadSelectedCpuSets incorrectly referenced SYSTEM_CPU_SET_INFORMATION by index, while it is specifically forbidden by the structure docs.
2. An example for Reducing the cost of cache coherence with last level cache also did the above mistake, but the code did not even compile to begin with. I fixed the code snippet so it compiles, does less copies, and does not misuse SYSTEM_CPU_SET_INFORMATION. This code is still sub-optimal, but now it at least works.

Fixes #3025.

[prmerger-automator]

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[learn-build-service-prod]

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File	Status	Preview URL	Details
uwp/xbox-apps/cpusets-games.md	✅Succeeded

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