Auto merge of #12388 - kilobtye:textarea2, r=pcwalton

Let textarea wrap lines

<!-- Please describe your changes on the following line: -->
1. Change textarea's style from white-space: pre to white-space: pre-wrap.
2. Display insertion point when a line is wrapped.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #10053 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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resources/servo.css

@@ -9,7 +9,7 @@ input {
   color: black;
   font-family: sans-serif;
   font-size: 0.8333em;
-  white-space: nowrap;
+  white-space: pre;
   text-align: left;
   line-height: 1.8;
 }
@@ -24,7 +24,7 @@ textarea {
   color: black;
   font-family: sans-serif;
   font-size: 0.8333em;
-  white-space: pre;
+  white-space: pre-wrap;
 }
 
 input::selection,