PromptFeature may use invalid request code

[csadilek]

Looks like we're using IDs as request codes and there's no guarantee that they are valid: R.id.mozac_feature_prompts_file_picker_activity_request_code

See Sentry:
java.lang.IllegalArgumentException: Can only use lower 16 bits for requestCode

https://sentry.prod.mozaws.net/operations/fenix-nightly/issues/6540015/?environment=fenixNightly

┆Issue is synchronized with this Jira Task

[Amejia481]

cc: @NotWoods

[NotWoods]

Argh, I tried to use ids to manage our request codes. I'll revert these changes.