Auto merge of #17739 - jdm:no-vendor-prefixed-errors, r=emilio

Suppress CSS parser errors for vendor-prefixed properties.

This matches the behaviour of Gecko's CSS parser.

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #17736
- [X] There are tests for these changes

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ports/geckolib/error_reporter.rs

@@ -233,7 +233,8 @@ impl<'a> ErrorHelpers<'a> for ContextualParseError<'a> {
                 ErrorString::Ident(namespace),
 
             (_, CssParseError::Custom(SelectorParseError::Custom(
-                StyleParseError::UnknownProperty(property)))) =>
+                StyleParseError::PropertyDeclaration(
+                    PropertyDeclarationParseError::UnknownProperty(property))))) =>
                 ErrorString::Ident(property),
 
             (_, CssParseError::Custom(SelectorParseError::Custom(