fix(js): export all-objects converters from module.exports

[schani]

Bug

With --converters all-objects, the JavaScript renderer generates
toX/xToJson converter functions for every object type in the schema, not
just the top-level types. However, module.exports only ever listed the
top-level converters, so the extra per-object converters were generated but
inaccessible/unusable to callers of the module.

Repro:

node dist/index.js --src-lang schema json.schema --lang js --runtime-typecheck --acronym-style pascal --converters all-objects -o output.js

produced toData123/data123ToJson functions in the file body, but
module.exports only contained the top-level toOutput/outputToJson.

Root cause

In packages/quicktype-core/src/language/JavaScript/JavaScriptRenderer.ts,
emitConvertModuleBody() already branches on
this._jsOptions.converters === ConvertersOptions.AllObjects to decide
whether to iterate forEachObject or forEachTopLevel when emitting the
converter functions themselves. emitModuleExports() did not have the same
branch — it unconditionally used forEachTopLevel, so the export list never
matched what was actually generated when all-objects was selected.

Fix

emitModuleExports() now mirrors emitConvertModuleBody()'s switch on
this._jsOptions.converters, using forEachObject for
ConvertersOptions.AllObjects and forEachTopLevel otherwise (unchanged
default behavior).

Test coverage

• Added test/inputs/json/samples/issue-1655.json, a sample with a nested
  object type, wired into test/languages.ts's
  JavaScriptLanguage.quickTestRendererOptions with
  { converters: "all-objects" } (same tuple pattern already used for other
  targeted regression samples like pokedex.json).
• Extended test/fixtures/javascript/main.js to additionally call the
  nested object's exported converter (toData123/data123ToJson) when the
  generated source defines it, so the fixture driver actually exercises the
  export and fails with a runtime TypeError if it's missing.
• Verified locally that reverting just the renderer fix makes this new
  fixture fail (TypeError: TopLevel.toData123 is not a function), and that
  with the fix in place it passes.

Verification

• npm run build passes.
• QUICKTEST=true FIXTURE=javascript script/test — all 59 JavaScript
  fixture tests pass, including the new issue-1655.json case run with
  converters: all-objects.
• Manually re-ran the exact repro command from the issue and confirmed
  module.exports now includes data123ToJson/toData123 alongside the
  top-level converters.
• Full CI suite (other languages, lint, etc.) is left to GitHub Actions.

Fixes #1655

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