Format all Nix files using the officially approved formatter,
making the CI check introduced in the previous commit succeed:
nix-build ci -A fmt.check
This is the next step of the of the [implementation](https://github.com/NixOS/nixfmt/issues/153)
of the accepted [RFC 166](https://github.com/NixOS/rfcs/pull/166).
This commit will lead to merge conflicts for a number of PRs,
up to an estimated ~1100 (~33%) among the PRs with activity in the past 2
months, but that should be lower than what it would be without the previous
[partial treewide format](https://github.com/NixOS/nixpkgs/pull/322537).
Merge conflicts caused by this commit can now automatically be resolved while rebasing using the
[auto-rebase script](8616af08d9/maintainers/scripts/auto-rebase).
If you run into any problems regarding any of this, please reach out to the
[formatting team](https://nixos.org/community/teams/formatting/) by
pinging @NixOS/nix-formatting.
This introduces extra escaping for $NIX_STORE that gets interpolated
into a PCRE. The escaping is performed using a standard Perl function
"quotemeta" (see "perldoc -f quotemeta" for reference). The same value
is also used in sed regex which uses POSIX basic regular expressions
instead of PCRE, so it needs fewer characters to be escaped. It should
not cause much problem to not change sed invocation, but I replace it
with equivalent Perl expression (actually the behavior is changed to not
output a newline character after the matched output).
