Use platform_env instead of dart_env in package:intl tests.
Use platform_env instead of dart_env in package:intl tests.

The VM is about to switch to use the CFE's constant evaluator. This change
will break const.fromEnvironment on modular builds (which affects blaze and build_runner).

Because the only purpose of these definitions was to pass arguments to tests, we can
replace them with a runtime Platform.environment variable.

Context: b/129881700 and https://github.com/dart-lang/sdk/issues/36513
PiperOrigin-RevId: 242916034

dart-lang/intl