This is a Fuchsia change to prepare for future changes to the SDK. LogSink and InspectSink will soon be routed through dictionaries, rather than explicitly. For RealmBuilders, we need to route both the dictionary and the protocol (to preserve compatibility). For CML files, we need to use the shards in the SDK instead of using explicit routes. Once the SDK shard is updated, then all SDK consumers should receive new routes. However, not everyone will necessarily be updated at the same time, which is the reason for keeping compatibility routes in RealmBuilder (to prepare for the soft transition).

b/394681733

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.
• [(Google employee)] 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 ///).
• [X (exempt, SDK mechanical change only)] 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.
• [X (unable to test on Fuchsia, I believe it has to be merged to be tested)] All existing and new tests are passing.

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