Add assert messages and print bad argument values in asserts (#5216)

Enabled the `missing_assert_message` lint

* [x] I have followed the instructions in the PR template

---------

Co-authored-by: Lucas Meurer <lucasmeurer96@gmail.com>

crates/epaint/src/text/font.rs

@@ -91,8 +91,14 @@ impl FontImpl {
         scale_in_pixels: f32,
         tweak: FontTweak,
     ) -> Self {
-        assert!(scale_in_pixels > 0.0);
-        assert!(pixels_per_point > 0.0);
+        assert!(
+            scale_in_pixels > 0.0,
+            "scale_in_pixels is smaller than 0, got: {scale_in_pixels:?}"
+        );
+        assert!(
+            pixels_per_point > 0.0,
+            "pixels_per_point must be greater than 0, got: {pixels_per_point:?}"
+        );
 
         use ab_glyph::{Font, ScaleFont};
         let scaled = ab_glyph_font.as_scaled(scale_in_pixels);
@@ -264,7 +270,7 @@ impl FontImpl {
     }
 
     fn allocate_glyph(&self, glyph_id: ab_glyph::GlyphId) -> GlyphInfo {
-        assert!(glyph_id.0 != 0);
+        assert!(glyph_id.0 != 0, "Can't allocate glyph for id 0");
         use ab_glyph::{Font as _, ScaleFont};
 
         let glyph = glyph_id.with_scale_and_position(

crates/epaint/src/text/text_layout.rs

@@ -529,7 +529,7 @@ fn halign_and_justify_row(
         (num_leading_spaces, row.glyphs.len() - num_trailing_spaces)
     };
     let num_glyphs_in_range = glyph_range.1 - glyph_range.0;
-    assert!(num_glyphs_in_range > 0);
+    assert!(num_glyphs_in_range > 0, "Should have at least one glyph");
 
     let original_min_x = row.glyphs[glyph_range.0].logical_rect().min.x;
     let original_max_x = row.glyphs[glyph_range.1 - 1].logical_rect().max.x;
@@ -898,7 +898,10 @@ fn add_hline(point_scale: PointScale, [start, stop]: [Pos2; 2], stroke: Stroke,
     } else {
         // Thin lines often lost, so this is a bad idea
 
-        assert_eq!(start.y, stop.y);
+        assert_eq!(
+            start.y, stop.y,
+            "Horizontal line must be horizontal, but got: {start:?} -> {stop:?}"
+        );
 
         let min_y = point_scale.round_to_pixel(start.y - 0.5 * stroke.width);
         let max_y = point_scale.round_to_pixel(min_y + stroke.width);

crates/epaint/src/text/text_layout_types.rs

@@ -892,7 +892,7 @@ impl Galley {
             }
             ccursor_it.index += row.char_count_including_newline();
         }
-        debug_assert!(ccursor_it == self.end());
+        debug_assert!(ccursor_it == self.end(), "Cursor out of bounds");
 
         if let Some(last_row) = self.rows.last() {
             LayoutCursor {