Add a from_line_height constructor function to TextFont. (#20335)

# Objective

`TextFont` has `from_font` and `from_font_size` constructors but is
missing one for line height.

## Solution

* Added a `from_line_height` constructor function to `TextFont`.
* Also added `From<Handle<Font>>` and `From<LineHeight>` impls.

We could also add a `From<f32>` for font size but I thought it might be
confusing. At some some point we want to add responsive text size
support, can do it then.

Author: ickshonpe

crates/bevy_text/src/text.rs

@@ -4,7 +4,7 @@ use bevy_color::Color;
 use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{prelude::*, reflect::ReflectComponent};
 use bevy_reflect::prelude::*;
-use bevy_utils::once;
+use bevy_utils::{default, once};
 use cosmic_text::{Buffer, Metrics};
 use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
@@ -315,6 +315,11 @@ impl TextFont {
         Self::default().with_font_size(font_size)
     }
 
+    /// Returns a new [`TextFont`] with the specified line height.
+    pub fn from_line_height(line_height: LineHeight) -> Self {
+        Self::default().with_line_height(line_height)
+    }
+
     /// Returns this [`TextFont`] with the specified font face handle.
     pub fn with_font(mut self, font: Handle<Font>) -> Self {
         self.font = font;
@@ -340,6 +345,21 @@ impl TextFont {
     }
 }
 
+impl From<Handle<Font>> for TextFont {
+    fn from(font: Handle<Font>) -> Self {
+        Self { font, ..default() }
+    }
+}
+
+impl From<LineHeight> for TextFont {
+    fn from(line_height: LineHeight) -> Self {
+        Self {
+            line_height,
+            ..default()
+        }
+    }
+}
+
 impl Default for TextFont {
     fn default() -> Self {
         Self {