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 *
The 2 seperate key and value arrays are replaced with a single struct pair
array that allows for a 2x reduction in loads/stores during element swaps
in the common case of same-sized keys and values.
