This patch adds support for opening a ConfigFile using a file
descriptor rather than trying to open a the file by name directly.
In contrast to the previous implementation, ConfigFile now always keeps
a reference to an open File and does not reopen it for writing.
This requires providing an additional argument to open functions if a
file gets opened based on its name and the user of the api intends to
write to the file in the future.
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 *
