Show inline completions inside the completion menu if both are available (#22093)

Screenshot:

![screenshot-2024-12-17-11 53
41@2x](https://github.com/user-attachments/assets/bace3d20-7175-4833-9326-7b859166c0e8)

Demo:


https://github.com/user-attachments/assets/70197042-4785-4e45-80fd-29d12e68333f



(Note for Joseph/Peter: this supersedes
https://github.com/zed-industries/zed/pull/22069)

Release Notes:
- Changed inline completions to show up inside the normal completions in
case LSP and inline-completions are available. In that case, the inline
completion will be the first entry in the menu and can be selected with
`<tab>`.

---------

Co-authored-by: Bennet <bennet@zed.dev>
Co-authored-by: Danilo <danilo@zed.dev>

assets/keymaps/default-linux.json

@@ -471,22 +471,13 @@
     }
   },
   {
-    "context": "Editor && !inline_completion && showing_completions",
+    "context": "Editor && showing_completions",
     "use_key_equivalents": true,
     "bindings": {
       "enter": "editor::ConfirmCompletion",
       "tab": "editor::ComposeCompletion"
     }
   },
-  {
-    "context": "Editor && inline_completion && showing_completions",
-    "use_key_equivalents": true,
-    "bindings": {
-      "enter": "editor::ConfirmCompletion",
-      "tab": "editor::ComposeCompletion",
-      "shift-tab": "editor::AcceptInlineCompletion"
-    }
-  },
   {
     "context": "Editor && inline_completion && !showing_completions",
     "use_key_equivalents": true,