Auto merge of #14538 - DominoTree:master, r=Manishearth,Wafflespeanut

Use LengthOrNormal for column-gap #14297

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14297 (github issue number if applicable).

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components/layout/multicol.rs

@@ -99,9 +99,11 @@ impl Flow for MulticolFlow {
         {
             let column_style = self.block_flow.fragment.style.get_column();
 
-            // `None` is 'normal': "UA-specified length. A value of 1em is suggested."
-            let column_gap = column_style.column_gap.0.unwrap_or_else(||
-                self.block_flow.fragment.style.get_font().font_size);
+            let column_gap = match column_style.column_gap {
+                Either::First(len) => len,
+                Either::Second(_normal) => self.block_flow.fragment.style.get_font().font_size,
+            };
+
             let mut column_count;
             if let Either::First(column_width) = column_style.column_width {
                 column_count =