TS: Add type discriminator support for slicing

[ryukzak]

• Support type discriminator in slicing — match slices by resourceType field
  • field-builder.ts: compute { resource: { resourceType: "<Type>" } } match pattern from FHIR type discriminator path and element type
  • profile-slices.ts: add typeDiscriminator flag to SliceDef; type-discriminated getters return items via as cast (no stripMatchKeys)
  • profile.ts: skip match-field omission in flat input types and stripMatchKeys import for type discriminator slices
• Update slices design doc: type discriminator status → Partial

Generated profile before (no type discriminator support — slices silently ignored):

// No PatientEntry/OrganizationEntry getters/setters generated

Generated profile after (ExampleTypedBundle with Bundle.entry sliced by resource type):

export type ExampleTypedBundle_Entry_PatientEntrySliceFlat = BundleEntry;
export type ExampleTypedBundle_Entry_OrganizationEntrySliceFlat = BundleEntry;

export class ExampleTypedBundleProfile {
    setPatientEntry(input?: ... | BundleEntry): this { ... }
    getPatientEntry(mode?: 'flat' | 'raw'): ... | undefined { ... }
    setOrganizationEntry(input?: ... | BundleEntry): this { ... }
    getOrganizationEntry(mode?: 'flat' | 'raw'): ... | undefined { ... }
}

Example & tests

• Add ExampleTypedBundle StructureDefinition with Patient/Organization entry slices
• Add profile-typed-bundle.test.ts demo covering create, set/get, validation, fluent chaining
• Add snapshot test for type-discriminated profile codegen output
• Deduplicate test StructureDefinitions (point at examples/ instead of test/assets/)
• Add Patient and Organization to local-package-folder tree shake
• Add test-local-package-folder-example target to Makefile