tab: Add setting to hide the close button entirely (#23880)

Closes #23744

Release Notes:

- Changed the `always_show_close_button` key to `show_close_button` and
introduced a new `hidden` value, that allows never displaying the close
button.

---------

Co-authored-by: Peter Tripp <peter@zed.dev>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: smit <0xtimsb@gmail.com>

docs/src/configuring-zed.md

@@ -784,7 +784,7 @@ List of `string` values
   "file_icons": false,
   "git_status": false,
   "activate_on_close": "history",
-  "always_show_close_button": false
+  "show_close_button": "hover"
 },
 ```
 
@@ -856,11 +856,37 @@ List of `string` values
 }
 ```
 
-### Always show the close button
+### Show close button
 
-- Description: Whether to always show the close button on tabs.
-- Setting: `always_show_close_button`
-- Default: `false`
+- Description: Controls the appearance behavior of the tab's close button.
+- Setting: `show_close_button`
+- Default: `hover`
+
+**Options**
+
+1.  Show it just upon hovering the tab:
+
+```json
+{
+  "show_close_button": "hover"
+}
+```
+
+2. Show it persistently:
+
+```json
+{
+  "show_close_button": "always"
+}
+```
+
+3. Never show it, even if hovering it:
+
+```json
+{
+  "show_close_button": "hidden"
+}
+```
 
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