editor: Respect multi_cursor_modifier setting when making columnar selections using mouse (#32273)

Closes https://github.com/zed-industries/zed/issues/31181

Release Notes:

- Added the `multi_cursor_modifier` setting to be respected when making
columnar selections using the mouse drag.

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

assets/settings/default.json

@@ -101,9 +101,12 @@
     // The second option is decimal.
     "unit": "binary"
   },
-  // The key to use for adding multiple cursors
-  // Currently "alt" or "cmd_or_ctrl"  (also aliased as
-  // "cmd" and "ctrl") are supported.
+  // Determines the modifier to be used to add multiple cursors with the mouse. The open hover link mouse gestures will adapt such that it do not conflict with the multicursor modifier.
+  //
+  // 1. Maps to `Alt` on Linux and Windows and to `Option` on MacOS:
+  //    "alt"
+  // 2. Maps `Control` on Linux and Windows and to `Command` on MacOS:
+  //    "cmd_or_ctrl" (alias: "cmd", "ctrl")
   "multi_cursor_modifier": "alt",
   // Whether to enable vim modes and key bindings.
   "vim_mode": false,