Fix spacing around hidden status bar items (#39992)

This is a follow-up PR to
https://github.com/zed-industries/zed/pull/39609, and attempts to
address hidden status bar items still contributing to the layout and
creating extra spacing.

![before using display:none theres extra spaces, afterwords the buttons
are always evenly
spaced](https://github.com/user-attachments/assets/3bd07837-5f6f-4ca1-8985-9f3cb8b6893d)

- 203cbd634bfb1489b8afa4952d9594615a956b77 Adds a `.none()` method to
the `gpui::Styled` helper trait, so that status items can set their
display type to none inside their `render` method.

- 249f06e3de63b0ab32814f20e7105d8e2b642f02 Applies `.none()` to all the
status items.

- ~~499f564906c88336608c81615b11ebc9ab43d832~~ At first I was adding an
`is_visible` method to the `StatusBarView` trait, which would be used to
skip status bar items which would just render an empty div anyway, but I
felt duplicating the conditions for hiding the buttons between the
status items `is_visible` and `render` methods could be an attraction
for bugs, so I tried to find another approach. This commit contains
those changes, reverted immediately (if the `is_visible` approach is
preferred I can bring it back!)

- f37cb75f0519ceea1f3e1cc4f97087a5cb34b0fd (bonus!) Adds a condition to
the vim mode indicator to avoid a leading space when there are no
pending keys.

Release Notes:

- N/A

crates/edit_prediction_button/src/edit_prediction_button.rs

@@ -72,17 +72,17 @@ impl Render for EditPredictionButton {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         // Return empty div if AI is disabled
         if DisableAiSettings::get_global(cx).disable_ai {
-            return div();
+            return div().hidden();
         }
 
         let all_language_settings = all_language_settings(None, cx);
 
         match all_language_settings.edit_predictions.provider {
-            EditPredictionProvider::None => div(),
+            EditPredictionProvider::None => div().hidden(),
 
             EditPredictionProvider::Copilot => {
                 let Some(copilot) = Copilot::global(cx) else {
-                    return div();
+                    return div().hidden();
                 };
                 let status = copilot.read(cx).status();