Disable CalculateNativeWinOcclusion for woa

Editor assessment

The subject names the flag and the platform: CalculateNativeWinOcclusion is disabled for Windows-on-ARM. That is precise but motivationally silent, and disabling a Chromium feature on a platform is exactly the kind of decision that deserves a recorded reason, whether rendering glitches, performance, or test instability. The ci type is plausible, no scope is attached, and no body or footers exist to supply the rationale. Hygiene is clean. Readers can see what changed and where, but must consult the diff or issue tracker to learn why, which limits the message's value.