Fixes [CSDK-622].
### Changes:
- Extracted `FileReader` to be able to use it in `ReceiptParser`
- Extracted `MockBundle` to be able to use it in `ReceiptParser`
- Added new `public` `ReceiptParser.fetchAndParseLocalReceipt()`, **only
to `ReceiptParser`** (this is not available through `RevenueCat`).
- Added tests for the new API
- Added new API to `ReceiptParserAPITester`
Initially I thought about moving `ReceiptFetcher` to the
`Receipt|Parser` target. Unfortunately that would require moving a whole
bunch of other dependencies (`OperationDispatcher`, etc, etc).
We have no easy way to create a third "Core" framework in which to place
these common dependencies, so that wouldn't be trivial.
This solution adds a much simpler version of `ReceiptFetcher` that
simply reads from `Bundle.appStoreReceiptURL`. As it's documented there,
under normal circumstances `SKReceiptRefreshRequest` is not required, so
this implementation should work for 99% of use cases, and so this way we
avoid increasing the.codebase complexity unnecessarily.
[CSDK-622]:
https://revenuecats.atlassian.net/browse/CSDK-622?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
NachoSoto