Deeply-curried functions are pretty error-prone in untyped languages
like Nix. This is a particularly bad case because
`top-level/splice.nix` *also* declares a makeScopeWithSplicing, but
it takes *two fewer arguments*.
Let's switch to attrset-passing form, to provide some minimal level
of sanity-checking.
`lib.extends hooks pythonPackagesFun` includes python which we want to
splice
what this fixes:
```
nix-repl> lib.elemAt pkgsCross.aarch64-multiplatform.python3Packages.xpybutil.nativeBuildInputs 0
«derivation /nix/store/39dkb51rciw6zwg0c2c44gpmpjapddxc-python3-aarch64-unknown-linux-gnu-3.10.12.drv»
```
to
```
nix-repl> lib.elemAt pkgsCross.aarch64-multiplatform.python3Packages.xpybutil.nativeBuildInputs 0
«derivation /nix/store/21ldw2dp26xvv9iyxn9x77a8yh4waqz5-python3-3.10.12.drv»
```
Before https://github.com/NixOS/nixpkgs/pull/194205 The keep python used to work by accident because self was passed from
__splicedPackages https://github.com/NixOS/nixpkgs/pull/196052/files#diff-44ce3495c4f983ce64dd47c86a9d3e77bad210b2709c098a3806998dcd9b000bR213
But now it does not work because overrideAttrs is used on python in
python-packages-base.nix
Preferably we would [ splice the hooks too ](https://github.com/NixOS/nixpkgs/pull/228139) but we cannot do that until [Package sets within derivations (i.e. python3.pkgs) are not spliced](https://github.com/NixOS/nixpkgs/issues/211340) is fixed, because people often use `python3.pkgs.wrapPython` in `nativeBuildInputs` (it's correct but python3.pkgs should be python3Packages to get splicing.
Remove the implicit dependency on `elixir` being somewhere in `PATH`.
Before:
```
$ nix build '.#elixir_1_15'
$ ./result/bin/mix --version
env: ‘elixir’: No such file or directory
```
After:
```
$ nix build '.#elixir_1_15'
$ ./result/bin/mix --version
Erlang/OTP 25 [erts-13.2.2.2] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]
Mix 1.15.2 (compiled with Erlang/OTP 25)
```
This was caused by the shebang interpreter directive being set to
`${coreutils}/bin/env elixir`, whereas now the `elixir` part is replaced
with the full path to the interpreter.
We can't get rid of the `${coreutils}/bin/env` part, because without it
all scripts are interpreted as shell scripts.
