fix(schema): use patternProperties as map value type

[schani]

Bug

An object schema with additionalProperties: false (or unset) plus
patternProperties was ignored entirely, so quicktype generated an empty
interface/class for that object instead of a map keyed by the pattern's
value type.

Minimal repro (from the issue, --src-lang schema --lang ts):

"a2": {
  "type": "object",
  "additionalProperties": false,
  "patternProperties": { "^.+$": { "type": "string" } }
}

Before:

export interface Schema {
    a2?: A2;
}
export interface A2 {
}

After:

export interface Schema {
    a2?: { [key: string]: string };
}

Same fix applies to C# (a2 now generates Dictionary<string, string>
instead of an empty class).

Root cause

packages/quicktype-core/src/input/JSONSchemaInput.ts only ever looked at
patternProperties["*"] (a narrow hack originally added for issue #976) and
only when additionalProperties was undefined. Any other pattern key, or
an explicit additionalProperties: false, meant patternProperties was
silently dropped, producing an object with no properties and no map type.

Fix

When additionalProperties is not true (quicktype can't represent
per-pattern keys, so it approximates all matching properties with a map
type), collect the schemas of all patternProperties entries — plus any
schema-valued additionalProperties — and use them as the object's
additional-properties (map value) type; combine multiple schemas with
anyOf. Also added schema.patternProperties !== undefined to the set of
schema fields that mark a JSON Schema node as needing type expansion, so
patternProperties-only nodes aren't skipped.

Test coverage

Added an end-to-end JSON Schema fixture:

• test/inputs/schema/pattern-properties-map.schema
• test/inputs/schema/pattern-properties-map.1.json

reproducing the issue's a1/a2 example (additionalProperties: true and
additionalProperties: false, both with patternProperties). This is
auto-discovered by the existing schema-fixture harness across all
languages that run schema fixtures.

Verification

• npm run build passes.
• npx vitest run test/unit — 169/169 passing.
• FIXTURE=schema-typescript script/test — 71/71 passing, including the
  new pattern-properties-map.schema fixture and the pre-existing
  go-schema-pattern-properties.schema fixture (confirming issue Infer property type based on patternProperties if pattern is .* #976's
  original scenario still works).
• Manually re-ran the issue's repro with --lang ts and --lang cs and
  confirmed both now emit a map type instead of an empty
  interface/class.
• schema-csharp fixture was not run locally (no dotnet toolchain in
  this environment); CI will validate it.

Fixes #1549

🤖 Generated with Claude Code

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