fix(java): generate named Java type for unknown type aliases

[jsklan]

Description

Linear ticket: Closes FER-8937

When an OpenAPI schema has no type and no properties (representing an "any" type), the Java SDK generator was dropping the named type definition entirely and inlining Object wherever it was referenced. This PR fixes the generator to emit a named wrapper class for unknown type aliases, consistent with how other alias types are handled.

Link to Devin Session
Requested by: @jsklan

Changes Made

Java generator (3 files)

1. SingleTypeGenerator.java — visitAlias() now also generates a wrapper class when the alias's underlying type is unknown (value.getAliasOf().isUnknown()), not only when wrappedAliases config is enabled or the alias comes from an error declaration.
2. PoetTypeNameMapper.java — visitNamed() no longer resolves unknown aliases to their underlying Object type. Previously all aliases were transparently resolved when wrappedAliases was false, causing the named type reference to be lost.
3. Cli.java (SDK) — The WrappedAlias interface is now also generated when any type declaration is an alias with an unknown aliasOf, since the generated wrapper class implements this interface.

Dynamic snippet generator (1 file)

4. DynamicTypeLiteralMapper.ts — convertNamed() now wraps the converted value in Type.of() when the alias's inner type reference is unknown, producing e.g. DocumentedUnknownType.of(new HashMap<>() {{ ... }}) instead of passing the raw HashMap directly.

Note: DynamicTypeMapper.ts was intentionally not changed. Type annotations for unknown aliases still resolve through to Object to avoid breaking generic type parameters (e.g. Map<String, Object> must not become Map<String, DocumentedUnknownType>). Only the literal value mapper wraps with .of().

• Updated generators/java/sdk/versions.yml with changelog entry
• Updated README.md generator (not applicable)

Testing

• Seed tests run for java-sdk / exhaustive fixture — all 14 configs pass
• Verified DocumentedUnknownType.java generated correctly across all configs
• Verified ObjectWithDocumentedUnknownType.java references DocumentedUnknownType (not Object)
• Verified snippet.json wraps unknown alias values with DocumentedUnknownType.of(...)
• All 295 CI checks passed including java-model and java-spring seed tests

Key review points

• WrappedAlias.java is now generated for any API that has unknown type aliases, even without wrappedAliases: true config. This is a net-new file in SDK output for affected APIs. Verify this is acceptable.
• The Cli.java change only covers the SDK generator. Verify whether java-model and java-spring generators (which share SingleTypeGenerator and PoetTypeNameMapper via generator-utils) need a similar WrappedAlias interface generation change in their own Cli classes.
• The generated DocumentedUnknownType.equals() does not null-guard this.value — consistent with existing AliasGenerator output but worth noting.

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✅ Devin Review: No Issues Found

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