…or (flutter#185651)

Updates Xcode SDK version from 16c5032a to 17c52 (Xcode 26.2), macOS
host from Mac-15.5|Mac-15.7 to Mac-15.7, and simulator runtime from
ios-18-2 to ios-26-2. Replaces 18.2 golden images with 26.2 goldens and
updates generate_builder_json.dart.

device_os remains iOS-18 for devicelab targets (physical devices not yet
upgraded).

Fixes flutter#172855

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Fixes] where supported.
- [ ] All existing and new tests are passing.

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