Refine word completions (#26779)

Follow-up of https://github.com/zed-industries/zed/pull/26410

* Extract word completions into their own, `editor::ShowWordCompletions`
action so those could be triggered independently of completions
* Assign `ctrl-shift-space` binding to this new action
* Still keep words returned along the completions as in the original PR,
but:
* Tone down regular completions' fallback logic, skip words when the
language server responds with empty list of completions, but keep on
adding words if nothing or an error were returned instead
    * Adjust the defaults to wait for LSP completions infinitely
* Skip "words" with digits such as `0_usize` or `2.f32` from completion
items, unless a completion query has digits in it

Release Notes:

- N/A

assets/keymaps/default-linux.json

@@ -362,6 +362,7 @@
       "ctrl-k ctrl-0": "editor::FoldAll",
       "ctrl-k ctrl-j": "editor::UnfoldAll",
       "ctrl-space": "editor::ShowCompletions",
+      "ctrl-shift-space": "editor::ShowWordCompletions",
       "ctrl-.": "editor::ToggleCodeActions",
       "ctrl-k r": "editor::RevealInFileManager",
       "ctrl-k p": "editor::CopyPath",

assets/keymaps/default-macos.json

@@ -466,6 +466,7 @@
       // Using `ctrl-space` in Zed requires disabling the macOS global shortcut.
       // System Preferences->Keyboard->Keyboard Shortcuts->Input Sources->Select the previous input source (uncheck)
       "ctrl-space": "editor::ShowCompletions",
+      "ctrl-shift-space": "editor::ShowWordCompletions",
       "cmd-.": "editor::ToggleCodeActions",
       "cmd-k r": "editor::RevealInFileManager",
       "cmd-k p": "editor::CopyPath",

assets/settings/default.json

@@ -1092,11 +1092,12 @@
     //
     // May take 3 values:
     // 1. "enabled"
-    //   Always fetch document's words for completions.
+    //   Always fetch document's words for completions along with LSP completions.
     // 2. "fallback"
-    //   Only if LSP response errors/times out/is empty, use document's words to show completions.
+    //   Only if LSP response errors or times out, use document's words to show completions.
     // 3. "disabled"
     //   Never fetch or complete document's words for completions.
+    //   (Word-based completions can still be queried via a separate action)
     //
     // Default: fallback
     "words": "fallback",
@@ -1107,8 +1108,8 @@
     // When fetching LSP completions, determines how long to wait for a response of a particular server.
     // When set to 0, waits indefinitely.
     //
-    // Default: 500
-    "lsp_fetch_timeout_ms": 500
+    // Default: 0
+    "lsp_fetch_timeout_ms": 0
   },
   // Different settings for specific languages.
   "languages": {