Combine types, enums, and unions in a single definitions map

[skonves]

Context

The Basketry IR currently stores named definitions in separate top-level arrays for types, enums, and unions. In practice, these definitions already share a single logical namespace, since names must be unique across all three collections. This means consumers must search multiple arrays to resolve a named definition, even though the result is conceptually just “a named definition in the service.”

Because Basketry IR is machine-oriented and intentionally optimized for reparsing and inspection, this split adds unnecessary traversal and symbol-resolution complexity. The IR should provide a single obvious place to look up any named definition.

Change

• Replace the top-level types, enums, and unions arrays with a single top-level definitions map.
• Use the definition name as the map key for direct lookup.
• Allow definitions values to be Type, Enum, SimpleUnion, or DiscriminatedUnion.
• Preserve each definition’s embedded name literal for source mapping and diagnostics.
• Rename ComplexValue to DefinedValue.
• Rename ComplexValue.typeName to DefinedValue.definitionName.

Consequences

• Named definition lookup becomes simpler and more efficient for rules, generators, and other tooling.
• Duplicate names across definition kinds become structurally impossible within a single service.
• The IR more clearly models named definitions as a single symbol table.
• Source-mapped name literals remain available after lookup for diagnostics and provenance.
• Requires Basketry validation to ensure each definition map key exactly matches definition.name.value.
• Consumers will need to migrate from array traversal to keyed definition lookup.
• This lays the groundwork for future definition kinds, such as aliases, without requiring another namespace redesign.