fixed flutter run for projects containing a watchOS companion

[tauu]

Description

As reported by @Henrik-glt in #51126 , when running a flutter app with a watchOS companion app on a physical iOS device using the flutter run command, the build currently breaks, although it works for simulated devices. The reason for this behaviour is, that when building for a physical device, the following parameters are set for xcodebuild:

ONLY_ACTIVE_ARCH=YES
ARCHS=$activeArchName //$activeArchName is the architecture of the iOS device.

Consequently xcodebuild will attempt to build the watchOS companion for the architecture of the iOS device, which is not possible. This PR fixes the issue by not setting the ARCHS parameter if a watchOS companion app is detected in the ios project.

Upon further investigation it seems that using ONLY_ACTIVE_ARCH=YES in combination with ARCHS is not an intended use case. See also the xcode build system guide. So I would propose to drop setting ARCHS for the build path having ONLY_ACTIVE_ARCH=YES. I performed just a few tests, but so far setting ONLY_ACTIVE_ARCH=YES was sufficient to limit the build to the architecture of the target device. Because more intensive tests might be required for this change, it could also be made in a separate PR.

Tests

I added the following tests:

• none

Checklist

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• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
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Breaking Change

Did any tests fail when you ran them? Please read [Handling breaking changes].

• No, no existing tests failed, so this is not a breaking change.

[fluttergithubbot]

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[jmagman]

LGTM