Better handling of Gnome desktop files

Gnome desktop support has a lot of folders in share that should be created
directly in share, rather than shared.

Add these folders to keg, and don't link any icon cache files into share.

Closes Homebrew/homebrew#20340.

Library/Homebrew/keg.rb

@@ -108,6 +108,8 @@ class Keg < Pathname
     share_mkpaths = %w[aclocal doc info locale man]
     share_mkpaths.concat((1..8).map { |i| "man/man#{i}" })
     share_mkpaths.concat((1..8).map { |i| "man/cat#{i}" })
+    # Paths used by Gnome Desktop support
+    share_mkpaths.concat %w[applications icons pixmaps sounds]
 
     # yeah indeed, you have to force anything you need in the main tree into
     # these dirs REMEMBER that *NOT* everything needs to be in the main tree
@@ -122,6 +124,9 @@ class Keg < Pathname
       when INFOFILE_RX then ENV['HOMEBREW_KEEP_INFO'] ? :info : :skip_file
       when LOCALEDIR_RX then :mkpath
       when *share_mkpaths then :mkpath
+      when /^icons\/.*\/icon-theme\.cache$/ then :skip_file
+      # all icons subfolders should also mkpath
+      when /^icons\// then :mkpath
       when /^zsh/ then :mkpath
       else :link
       end