Add a platform_summary utility to pick a summary. Externally this is
always the DDC SDK, internally other SDKs are supported - keep the
utility for consistency.
Add a sdk_summary argument to dart_codegen_action and fill it in
using the platform_summary utility.
Change the SDK's BUILD file to have a single summary since only the
strong summary is now supported. Update the DDC action to use it.
platform_summaryutility to pick a summary. Externally this is always the DDC SDK, internally other SDKs are supported - keep the utility for consistency.sdk_summaryargument todart_codegen_actionand fill it in using theplatform_summaryutility.