Include AppIntentsMetadataProcessor to mnemonic list for optimized remote cache and build execution

[thelvis4]

The action key for AppIntentsMetadataProcessor is unstable because its _app_intents_stub_binary input is non-deterministic. This causes frequent remote cache misses, causing the action to run locally.

[brentleyjones]

But is it's outputs deterministic? Because this more cares about the outputs. The AC for this being unstable just results in a new AC entry (which is small), but if the outputs are deterministic, it's worth caching them, right?

[thelvis4]

But is it's outputs deterministic? Because this more cares about the outputs. The AC for this being unstable just results in a new AC entry (which is small), but if the outputs are deterministic, it's worth caching them, right?

Currently, the json outputs from AppIntentsMetadataProcessor are also non-deterministic because the key order is unstable. There's #2761 to sort the keys. If that lands, it might be fine to keep remote caching.

In our case, we also noticed that ld64 produces non-deterministic linked debug binaries even for consecutive builds on the same repo path and commit, due to an unstable memory layout for .swiftmodule entries. As a result, the action runs locally every time because it never gets a remote AC hit.

For context, we disabled remote caching also to rule out these unstable AC keys as a cause of some cache replication issues we were investigating. I suspect this isn't an issue for folks using a deterministic linker like lld or for those with different remote cache configurations.