Use defaults for unchanged TextStyle fields (#14918)

This PR updates a number of spots where we were setting all of the
`TextStyle` fields even if we were not changing the values from the
defaults.

We now use `..Default::default()`.

Release Notes:

- N/A

crates/assistant/src/inline_assistant.rs

@@ -22,9 +22,9 @@ use futures::{
     SinkExt, Stream, StreamExt,
 };
 use gpui::{
-    point, AppContext, EventEmitter, FocusHandle, FocusableView, FontStyle, Global, HighlightStyle,
-    Model, ModelContext, Subscription, Task, TextStyle, UpdateGlobal, View, ViewContext, WeakView,
-    WhiteSpace, WindowContext,
+    point, AppContext, EventEmitter, FocusHandle, FocusableView, Global, HighlightStyle, Model,
+    ModelContext, Subscription, Task, TextStyle, UpdateGlobal, View, ViewContext, WeakView,
+    WindowContext,
 };
 use language::{Buffer, Point, Selection, TransactionId};
 use language_model::{LanguageModelRequest, LanguageModelRequestMessage, Role};
@@ -1864,12 +1864,8 @@ impl PromptEditor {
             font_features: settings.ui_font.features.clone(),
             font_size: rems(0.875).into(),
             font_weight: settings.ui_font.weight,
-            font_style: FontStyle::Normal,
             line_height: relative(1.3),
-            background_color: None,
-            underline: None,
-            strikethrough: None,
-            white_space: WhiteSpace::Normal,
+            ..Default::default()
         };
         EditorElement::new(
             &self.editor,