nix print-dev-env: Add --json flag

nix develop: Make bash environment parsing more robust

Instead have get-env.sh dump the bash environment as JSON. This should
be a lot less error-prone.

Fixes #4992.

Fix the `name` attribute in builtins.fetchGit

Accidentally broken by 7e5c79a2

Add a name attribute to the fetchers

We need to support it for the “old” fetch* functions for backwards
compatibility, but we don’t need it for fetchTree (as it’s a new
function).
Given that changing the `name` messes-up the content hashing, we can
just forbid passing a custom `name` argument to it

Apply OS checks to host platform, not build

flake.nixConfig: fix flake-registry config settings

Fixes this random failure:

    error: hash mismatch in fixed-output derivation '/tmp/nix-shell.EUgAVU/nix-test/tests/check/store/sfps3l3c5n7dabpx34kigxnfhmrwk2h6-dummy.drv':
             specified: sha256-47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=
                got:    sha256-0qhPS4tlCTfsj3PNi+LHSt1akRumTfJ0WO2CKdqASiY=

which happens because multiple tests were writing to ./dummy.

Fix #3388

Fix wrong hash var for aarch64-darwin binary

libcmd/installables: implement completion for Nix expressions passed via `-f`

Allow scp-style uris in `fetchgit`

doc: builtins: use a definition list

Add a fish completion script

Improve machine store URI parsing

Fix devShell handling of env values including @ and %

Prefer to throw specific errors

Fix #5303

Respect TERM=dumb more consistently

upload-release.pl: add aarch64-darwin