gpui: Add text alignment (#24090)

Adds a text property for controlling left, center, or right text
alignment.

#8792 should stay open since this doesn't add support for `justify`
(which would require a much bigger change since this can just alter the
origin of each line, but justify requires changing spacing, whereas
justify requires changes to each platform's shaping code).

Release Notes:

- N/A

crates/gpui/src/style.rs

@@ -293,6 +293,20 @@ pub enum TextOverflow {
     Ellipsis(&'static str),
 }
 
+/// How to align text within the element
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
+pub enum TextAlign {
+    /// Align the text to the left of the element
+    #[default]
+    Left,
+
+    /// Center the text within the element
+    Center,
+
+    /// Align the text to the right of the element
+    Right,
+}
+
 /// The properties that can be used to style text in GPUI
 #[derive(Refineable, Clone, Debug, PartialEq)]
 #[refineable(Debug)]
@@ -335,6 +349,10 @@ pub struct TextStyle {
 
     /// The text should be truncated if it overflows the width of the element
     pub text_overflow: Option<TextOverflow>,
+
+    /// How the text should be aligned within the element
+    pub text_align: TextAlign,
+
     /// The number of lines to display before truncating the text
     pub line_clamp: Option<usize>,
 }
@@ -362,6 +380,7 @@ impl Default for TextStyle {
             strikethrough: None,
             white_space: WhiteSpace::Normal,
             text_overflow: None,
+            text_align: TextAlign::default(),
             line_clamp: None,
         }
     }