TS: Split slice flat types into SliceFlat/SliceFlatAll with discriminator literals

[ryukzak]

Summary

• Split slice flat types into SliceFlat (setter input) and SliceFlatAll (getter return with discriminators)
• SliceFlat — no discriminator fields, used as setter parameter
• SliceFlatAll — extends SliceFlat with readonly discriminator literal types, returned by flat getter
• Flat getter now returns the full element (including discriminators) instead of stripping them
• Long SliceMatch static fields and SliceFlatAll types are split across multiple lines
• Skip discriminator intersection for constrained choice slices (field name collisions) and plain object match values (partial object conflicts)

Before:

export type VSCatSliceFlat = Omit<CodeableConcept, "coding">;

// setter
setVSCat(input?: VSCatSliceFlat | CodeableConcept): this
// getter stripped discriminators at runtime
getVSCat(): VSCatSliceFlat | undefined  // { text: "Vital Signs" }

After:

export type VSCatSliceFlat = Omit<CodeableConcept, "coding">;
export type VSCatSliceFlatAll = VSCatSliceFlat & {
    readonly coding: [{ code: "vital-signs"; system: "http://..." }];
}

// setter accepts SliceFlat (no discriminators, auto-applied)
setVSCat(input?: VSCatSliceFlat | CodeableConcept): this
// getter returns SliceFlatAll (includes discriminator values)
getVSCat(): VSCatSliceFlatAll | undefined  // { text: "Vital Signs", coding: [...] }

Closes #122