Auto merge of #13724 - NamsooCho:font_variant_position, r=Manishearth

font_variant_position

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added 'font-variant-position' property to font.mako-rs
---
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- [X] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #13669 (github issue number if applicable).

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components/style/properties/longhand/font.mako.rs

@@ -353,3 +353,11 @@ ${helpers.single_keyword("font-kerning",
                          "auto none normal",
                          products="gecko",
                          animatable=False)}
+
+${helpers.single_keyword("font-variant-position",
+                         "normal sub super",
+                         products="gecko",
+                         gecko_ffi_name="mFont.variantPosition",
+                         gecko_constant_prefix="NS_FONT_VARIANT_POSITION",
+                         animatable=False)}
+