fix(typescript-input): preserve declared property order (#898)

[schani]

Bug

Given TypeScript class input:

class A {
    name: string;
    age: number;
}

quicktype's Swift output alphabetized the fields instead of preserving
declaration order:

struct A {
    let age: Double
    let name: String
}

This breaks the generated memberwise initializer's parameter order and,
more generally, silently reorders any output that's sensitive to property
order.

Root cause

packages/quicktype-typescript-input/src/index.ts invokes
typescript-json-schema to convert TypeScript sources into a JSON Schema,
but never passed the propOrder setting. Without it, typescript-json-schema
emits no propertyOrder metadata on schema definitions, so downstream
JSONSchemaInput has no order information to work with and falls back to
alphabetical/insertion order from the schema object.

quicktype already has a mechanism for this: JSONSchemaInput reads an
optional quicktypePropertyOrder field off each schema definition
(packages/quicktype-core/src/input/JSONSchemaInput.ts), it just was never
populated for TypeScript-source input.

Fix

• Enable propOrder: true in the typescript-json-schema settings.
• Copy the emitted propertyOrder array from each schema definition onto
  quicktypePropertyOrder, which JSONSchemaInput already consumes.

Tests

Added a regression test in test/unit/typescript-input.test.ts that compiles
a TypeScript class through schemaForTypeScriptSources and then through
quicktype to Swift, asserting name is emitted before age, matching
declaration order.

This bug is specific to the "TypeScript source as input" path
(--src-lang typescript), which starts from .ts files rather than JSON or
JSON Schema fixtures, so it isn't expressible via the repo's JSON/JSON Schema
fixture harness (test/inputs/json, test/inputs/schema) — a unit test is
the appropriate coverage here per repo conventions.

Verification

• npm run build passes.
• npx vitest run — all 171 unit tests pass (26 files), including the new
  regression test.
• Manual repro: node dist/index.js --lang swift --src-lang typescript A.ts
  with the class above now emits name before age in the generated
  Swift struct.

Fixes #898

🤖 Generated with Claude Code