Overriding the componentized build (backport #12503)

[mergify]

Motivation

• Keep Nix and Nixpkgs packaging harmonized
• Multiple user requests for adding patches
  • nixVersions.nix_2_26: init at 2.26.1 nixpkgs#375856 (comment)
  • Matrix: Nix Package Manager Development
  • https://discourse.nixos.org/t/overriding-the-nix-2-26-componentized-build/60428
• Make it easier for Nixpkgs to use a fetched source when vendoring or maintaining a copy of these packaging expressions

Changes

This adds

• overrideSource, switching to Nixpkgs-style packaging with a fetched source
• appendPatches, which applies patches to all components
• overrideAllMesonComponents to do arbitrary stuff to the meson-based builds (can be used to target individual derivations as well, with a conditional on prevAttrs.name)

Context

• Probably depended on Restore detailed Nix CLI version #12498

• Closes Packaging: support for patching the nix package #12472

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This is an automatic backport of pull request #12503 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of cca0140 has failed:

On branch mergify/bp/2.26-maintenance/pr-12503
Your branch is up to date with 'origin/2.26-maintenance'.

You are currently cherry-picking commit cca01407a.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   flake.nix
	modified:   packaging/components.nix

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   packaging/dependencies.nix

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally