emacs: migrate build-support/emacs to applications/editors/emacs/build-support

As a consequence of restrictions imposed by RFC 140 - Simple Package Paths [1]
-, files related to a package should be confined on the package directory.

Certainly this restriction does not apply to packages outside by-name hierarchy.

Nonetheless, this is an interesting organization heuristics: things that affect
Emacs should be confined inside Emacs directory. Besides a future migration, the
"debuggability" of a framework is way more enhanced when we know how to find all
its files.

A similar task was done before, when RFC 140 was not a thging yet - namely, the
migration of emacs-modes to elisp-packages [2].

[1] https://github.com/NixOS/rfcs/pull/140
[2] https://github.com/NixOS/nixpkgs/pull/123859

pkgs/applications/editors/emacs/elisp-packages/elpa-devel-packages.nix

@@ -32,7 +32,7 @@ self: let
     });
   };
 
-  elpaBuild = import ../../../../build-support/emacs/elpa.nix {
+  elpaBuild = import ../build-support/elpa.nix {
     inherit lib stdenv texinfo writeText gcc;
     inherit (self) emacs;
   };

pkgs/applications/editors/emacs/elisp-packages/elpa-packages.nix

@@ -32,7 +32,7 @@ self: let
     });
   };
 
-  elpaBuild = import ../../../../build-support/emacs/elpa.nix {
+  elpaBuild = import ../build-support/elpa.nix {
     inherit lib stdenv texinfo writeText gcc;
     inherit (self) emacs;
   };

pkgs/top-level/all-packages.nix

@@ -1288,7 +1288,10 @@ with pkgs;
 
   mpsolve = libsForQt5.callPackage ../applications/science/math/mpsolve { };
 
-  nixBufferBuilders = import ../build-support/emacs/buffer.nix { inherit lib writeText; inherit (emacs.pkgs) inherit-local; };
+  nixBufferBuilders = import ../applications/editors/emacs/build-support/buffer.nix {
+    inherit lib writeText;
+    inherit (emacs.pkgs) inherit-local;
+  };
 
   nix-gitignore = callPackage ../build-support/nix-gitignore { };
 

pkgs/top-level/emacs-packages.nix

@@ -47,7 +47,7 @@ let
     inherit lib pkgs;
   };
 
-  emacsWithPackages = { pkgs, lib }: pkgs.callPackage ../build-support/emacs/wrapper.nix {
+  emacsWithPackages = { pkgs, lib }: pkgs.callPackage ../applications/editors/emacs/build-support/wrapper.nix {
     inherit (pkgs.xorg) lndir;
     inherit lib;
   };
@@ -77,11 +77,11 @@ in makeScope pkgs'.newScope (self: makeOverridable ({
       };
     });
 
-    trivialBuild = pkgs.callPackage ../build-support/emacs/trivial.nix {
+    trivialBuild = pkgs.callPackage ../applications/editors/emacs/build-support/trivial.nix {
       inherit (self) emacs;
     };
 
-    melpaBuild = pkgs.callPackage ../build-support/emacs/melpa.nix {
+    melpaBuild = pkgs.callPackage ../applications/editors/emacs/build-support/melpa.nix {
       inherit (self) emacs;
     };