Auto merge of #17455 - canaltinova:webkit-displays, r=Manishearth

Implement webkit prefixed values for display property

Added -webkit-{flex,inline-flex} values as flex, inline-flex. I didn't do this gecko only since that doesn't require anything in layout side.

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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 #15400 (github issue number if applicable).

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

@@ -19,9 +19,10 @@
         values = """inline block inline-block
             table inline-table table-row-group table-header-group table-footer-group
             table-row table-column-group table-column table-cell table-caption
-            list-item flex inline-flex
-            none
+            list-item none
         """.split()
+        webkit_prefixed_values = "flex inline-flex".split()
+        values += webkit_prefixed_values
         if product == "gecko":
             values += """grid inline-grid ruby ruby-base ruby-base-container
                 ruby-text ruby-text-container contents flow-root -webkit-box
@@ -121,6 +122,11 @@
                     Ok(computed_value::T::${to_rust_ident(value)})
                 },
             % endfor
+            % for value in webkit_prefixed_values:
+                "-webkit-${value}" => {
+                    Ok(computed_value::T::${to_rust_ident(value)})
+                },
+            % endfor
         }
     }