Update file vs folder open keymaps on macos/linux to match windows (#44598)

Closes #44597

Matches what was done here:

https://github.com/zed-industries/zed/pull/44409/commits/55dfbaca685fc466efedace55527b9d12ab67950#diff-cc832e840d61526768bb4acec7645a71e8b160a65a30e7ce9e9c51762b58199a

Release Notes:

- Standardize Cmd-O = open file, Cmd-K Cmd-O = open folder across
operating systems.

---------

Co-authored-by: Lukas Wirth <me@lukaswirth.dev>

assets/keymaps/default-linux.json

@@ -25,7 +25,8 @@
       "ctrl-shift-w": "workspace::CloseWindow",
       "shift-escape": "workspace::ToggleZoom",
       "open": "workspace::Open",
-      "ctrl-o": "workspace::Open",
+      "ctrl-o": "workspace::OpenFiles",
+      "ctrl-k ctrl-o": "workspace::Open",
       "ctrl-=": ["zed::IncreaseBufferFontSize", { "persist": false }],
       "ctrl-+": ["zed::IncreaseBufferFontSize", { "persist": false }],
       "ctrl--": ["zed::DecreaseBufferFontSize", { "persist": false }],
@@ -814,7 +815,6 @@
       "ctrl-]": "agent::CycleNextInlineAssist",
       "ctrl-shift-enter": "inline_assistant::ThumbsUpResult",
       "ctrl-shift-backspace": "inline_assistant::ThumbsDownResult"
-
     }
   },
   {