5a3f245710
Ensure that all Objective-C code in the codebase is being built with the standard set of Flutter Objective-C compiler flags with ARC enabled. Also bumps the cflags config up to the top of the first block within each target in which Objective-C sources appear, so that the location is consistent. Migrates The following targets to ARC, which had been missed in previous passes since they didn't declare the standard Flutter Obj-C[++] cflags: * `//flutter/fml:fml_unittests` * `//flutter/impeller/golden_tests:metal_screenshot` * `//flutter/impeller/playground:playground` * `//flutter/impeller/backend/metal:metal` * `//flutter/impeller/backend/metal:metal_unittests` * `//shell/gpu:gpu_surface_metal_unittests` * `//flutter/shell/platform/embedder:embedder_unittests` This patch includes no semantic changes. Issue: https://github.com/flutter/flutter/issues/137801 [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style