treewide: add meta.mainProgram to editors

pkgs/applications/editors/emacs/sources.nix

@@ -32,6 +32,7 @@ let
       matthewbauer
     ];
     platforms = lib.platforms.all;
+    mainProgram = "emacs";
   };
 in
 {

pkgs/applications/editors/geany/default.nix

@@ -64,5 +64,6 @@ stdenv.mkDerivation rec {
     license = licenses.gpl2;
     maintainers = with maintainers; [ frlan ];
     platforms = platforms.all;
+    mainProgram = "geany";
   };
 }

pkgs/applications/editors/gedit/default.nix

@@ -96,5 +96,6 @@ stdenv.mkDerivation rec {
     maintainers = [ ];
     license = licenses.gpl2Plus;
     platforms = platforms.unix;
+    mainProgram = "gedit";
   };
 }

pkgs/applications/editors/micro/default.nix

@@ -41,5 +41,6 @@ buildGoModule rec {
     description = "Modern and intuitive terminal-based text editor";
     license = licenses.mit;
     maintainers = with maintainers; [ dtzWill ];
+    mainProgram = "micro";
   };
 }

pkgs/applications/editors/nano/default.nix

@@ -75,5 +75,6 @@ in stdenv.mkDerivation rec {
     license = licenses.gpl3Plus;
     maintainers = with maintainers; [ joachifm nequissimus ];
     platforms = platforms.all;
+    mainProgram = "nano";
   };
 }

pkgs/applications/editors/vim/common.nix

@@ -27,5 +27,6 @@ rec {
     license     = licenses.vim;
     maintainers = with maintainers; [ das_j equirosa ];
     platforms   = platforms.unix;
+    mainProgram = "vim";
   };
 }