SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

This adds unit tests for IOS/ESFormats, and in particular, for the
TMDReader. It is tested using invalid TMDs (to check IsValid()) and
two valid, properly signed TMDs.

Things which are now tested:

* Title type helper functions.
* TMDReader: Validity check.
* TMDReader: General information returned by the Get*() methods.
* TMDReader: Raw TMD and generated TMD view, compared against IOS.
* TMDReader: Game ID generation code (which is Dolphin specific).
* TMDReader: Content information: getting by ID/index, order, metadata.