Add Label::halign (emilk#4975)

Function to specify `Align` to `Label`

There are cases where you want to display `Label` on the left or right
regardless of other `Layout` specifications.

Before : Note the part showing the rust source code.

![20240818-1](https://github.com/user-attachments/assets/a08f7594-1ec1-4c6a-b96d-1a5f735d02c1)

After : Note the part showing the rust source code.

![20240818-2](https://github.com/user-attachments/assets/807ff9cf-f8cd-4415-9c78-b62869d1696d)

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

Author: 2 people

crates/egui/src/widgets/label.rs

@@ -26,6 +26,7 @@ pub struct Label {
     wrap_mode: Option<TextWrapMode>,
     sense: Option<Sense>,
     selectable: Option<bool>,
+    halign: Option<Align>,
 }
 
 impl Label {
@@ -35,6 +36,7 @@ impl Label {
             wrap_mode: None,
             sense: None,
             selectable: None,
+            halign: None,
         }
     }
 
@@ -76,6 +78,13 @@ impl Label {
         self
     }
 
+    /// Sets the horizontal alignment of the Label to the given `Align` value.
+    #[inline]
+    pub fn halign(mut self, align: Align) -> Self {
+        self.halign = Some(align);
+        self
+    }
+
     /// Can the user select the text with the mouse?
     ///
     /// Overrides [`crate::style::Interaction::selectable_labels`].
@@ -211,7 +220,7 @@ impl Label {
                 layout_job.halign = Align::LEFT;
                 layout_job.justify = false;
             } else {
-                layout_job.halign = ui.layout().horizontal_placement();
+                layout_job.halign = self.halign.unwrap_or(ui.layout().horizontal_placement());
                 layout_job.justify = ui.layout().horizontal_justify();
             };