Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.
This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.
Closes#8869
- Stick to a single unified way to use structs
- Make checksrc complain on 'typedef struct {'
- Allow them in tests, public headers and examples
- Let MD4_CTX, MD5_CTX, and SHA256_CTX typedefs remain as they actually
typedef different types/structs depending on build conditions.
Closes#5338