Enable Swift Package Manager by default on master channel

[loic-sharma]

Changes:

1. Enables Swift Package Manager by default on the main/master channel
2. Fixes tests that fail if Swift Package Manager is enabled

Corresponding docs change: flutter/website#10938

Addresses #151567

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[loic-sharma]

-g is an alias for --extern-only, description: Display only global (external) symbols.

[loic-sharma]

-U's description: Don't display undefined symbols. This isn't strictly necessary, it reduces the output of nm.

[loic-sharma]

We update the build settings of pods that depend on the Flutter framework (including transitive dependencies). This test only makes sense for CocoaPods, so we need to ensure we use CocoaPods. (We don't mutate the build settings of Swift packages, and Swift packages never depend on the Flutter framework)

For more context, see: #125610

[loic-sharma]

I recommend reviewing this diff with whitespace disabled: https://github.com/flutter/flutter/pull/152049/files?diff=split&w=1

[loic-sharma]

AppleTestUtils.getExportedSymbols is flutter_tools's helper for nm:

flutter/packages/flutter_tools/test/integration.shard/test_utils.dart

Lines 114 to 129 in 9181306

	static List<String> getExportedSymbols(String dwarfPath) {
	final ProcessResult nm = processManager.runSync(
	<String>[
	'nm',
	'--debug-syms', // nm docs: 'Show all symbols, even debugger only'
	'--defined-only',
	'--just-symbol-name',
	dwarfPath,
	'-arch',
	'arm64',
	],
	);
	final String nmOutput = (nm.stdout as String).trim();
	return nmOutput.isEmpty ? const <String>[] : nmOutput.split('\n');
	}
	}

This is effectively the same thing as the dumpSymbolTable helper I added to the devicelab package. AFAICT we don't share code between the tool and devicelab (I suspect this is intentional).

[jmagman]

Thank you for figuring out the nm details. LGTM!

[cbracken]

Reason for revert: iOS builds failing in post-submit

• Mac_ios integration_ui_ios_keyboard_resize
• Mac_ios native_assets_ios
• Mac_ios route_test_ios
• Mac_ios very_long_picture_scrolling_perf_ios__e2e_summary
• Mac_ios platform_channels_benchmarks_ios
• Mac_ios rrect_blur_perf_ios__timeline_summary
• Mac_ios complex_layout_scroll_perf_ios__timeline_summary
• Mac_ios new_gallery_skia_ios__transition_perf
• Mac_ios platform_views_scroll_perf_non_intersecting_impeller_ios__timeline_summary
• Mac_x64 plugin_lint_mac
• Mac_arm64 plugin_lint_mac