Increase minimum target iOS version from 11.0 to 12.0. Required to fix a crash that happens when iOS Networking.framework APIs are called. #136060

See details in flutter.dev/go/match-xcode-deployment-range.

• Set template and migrate apps to iOS 12 minimum #140478
• Cherry-pick Set template and migrate apps to iOS 12 minimum #140921
• Set ios_deployment_target to iOS 12.0 buildroot#808
• Roll buildroot to pick up iOS 12 engine#49542
• Update iOS minimum version documentation to 12.0 website#10001
• Remove iOS 12 availability checks engine#49771
• [various] Update minimum iOS versions to 12.0 packages#5902
• Once in stable, update 1p plugins to constrain to iOS version and Flutter stable version

See #101959 for when this was done 9 -> 11.