Hi, thank you for creating such a great framework!
I have a feature request which I think I can contribute, but let me check if you are interested in supporting it.

### Preflight Checklist
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* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for a feature request that matches the one I want to file, without success.

### Problem Description
The builtin spellchecker has been supported in https://github.com/electron/electron/pull/20692.
But it does not allow us to check spells programmatically, like [node-spellchecker](https://github.com/felixrieseberg/node-spellchecker)'s `isMisspelled` method.
Chrome's spellcheck_platform provides [CheckSpelling](https://chromium.googlesource.com/chromium/src/+/46ee392970e491fb9ee2523348e23222b40d5119/components/spellcheck/browser/spellcheck_platform.h#60) to do that exactly.

### Proposed Solution
Add a method to call `spellcheck_platform::CheckSpelling` like so:

```cc
#if BUILDFLAG(USE_BROWSER_SPELLCHECKER)
bool Session::CheckSpelling(const std::string& word) {
  if (spellcheck::UseBrowserSpellChecker()) {
    return spellcheck_platform::CheckSpelling(base::UTF8ToUTF16(word), 0);
  }
  return true;
}
#endif
```

in `shell/browser/api/atom_api_session.cc`.

It's simple and won't affect other features.

### Alternatives Considered
I don't know.

### Additional Information
None

Thanks!
shell/renderer/electron_renderer_client.cc
v8::Handle<v8::Context> context,
    content::RenderFrame* render_frame,
    int world_id) {
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
  NOTREACHED();
#else
  auto* isolate = context->GetIsolate();
  std::vector<v8::Local<v8::String>> isolated_bundle_params = {
      node::FIXED_ONE_BYTE_STRING(isolate, "nodeProcess"),
      node::FIXED_ONE_BYTE_STRING(isolate, "isolatedWorld"),
      node::FIXED_ONE_BYTE_STRING(isolate, "worldId")};
  auto* env = GetEnvironment(render_frame);
  if (!env)
    return;
  std::vector<v8::Local<v8::Value>> isolated_bundle_args = {
      env->process_object(),
      GetContext(render_frame->GetWebFrame(), isolate)->Global(),
      v8::Integer::New(isolate, world_id)};
  util::CompileAndCall(context, "electron/js2c/content_script_bundle",
                       &isolated_bundle_params, &isolated_bundle_args, nullptr);
#endif
}
node::Environment* ElectronRendererClient::GetEnvironment(