Auto merge of #18014 - emilio:bitfields, r=SimonSapin

stylo: We've had bitfield accessors for a while now.

This will allow my work in bug 1362338 to not break stylo.

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components/style/gecko_string_cache/mod.rs

@@ -156,11 +156,8 @@ impl WeakAtom {
     /// Returns the length of the atom string.
     #[inline]
     pub fn len(&self) -> u32 {
-        // FIXME(emilio): re-introduce bitfield accessors:
-        //
-        // https://github.com/servo/rust-bindgen/issues/519
         unsafe {
-            (*self.as_ptr())._bitfield_1 & 0x7FFFFFFF
+            (*self.as_ptr()).mLength()
         }
     }