Fuchsia api level 18 (flutter/engine#53115)

b/335285098
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engine/src/flutter/build/config/fuchsia/gn_configs.gni

@@ -25,7 +25,7 @@ declare_args() {
 # value to specify the API level the packages produced from this repository
 # should be targeting, e.g. in their top-level //.gn file. A value of -1
 # means that no API level will be passed to the tools that consumes it.
-fuchsia_target_api_level = 17
+fuchsia_target_api_level = 18
 
 # The SDK manifest file. This is useful to include as a dependency
 # for some targets in order to cause a rebuild when the version of the

engine/src/flutter/tools/fuchsia/build_fuchsia_artifacts_test.py

@@ -11,7 +11,7 @@ class BuildFuchsiaArtifactsTest(unittest.TestCase):
     # It's expected to update this test each time the fuchsia_target_api_level
     # in //flutter/build/config/fuchsia/gn_configs.gni is changed, so we don't
     # accidentally publish the artifacts with an incorrect api level suffix.
-    self.assertEqual(build_fuchsia_artifacts.ReadTargetAPILevel(), '17')
+    self.assertEqual(build_fuchsia_artifacts.ReadTargetAPILevel(), '18')
 
 
 if __name__ == '__main__':