servo: Merge #12364 - Make textarea scrollable (from kilobtye:textarea); r=jdm

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- [X] These changes fix #10058 (github issue number if applicable).

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Source-Repo: https://github.com/servo/servo
Source-Revision: 8c1be9b07ce2dbdd1fe696e3315bc4528846b419

servo/resources/servo.css

@@ -132,6 +132,10 @@ textarea {
   -servo-overflow-clip-box: content-box;
 }
 
+textarea {
+  overflow: auto;
+}
+
 /* https://html.spec.whatwg.org/multipage/rendering.html#the-details-and-summary-elements */
 details {
   display: block;