Since we were just repeatedly calling `->open()` on the same Core::File
no one was clearing it's internal buffer, which means hashing multiple
files in one go would result in different hashes than hashing each file
separately.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
