Auto merge of #24670 - glowe:add-crlf-to-boundary, r=Manishearth

Add CRLF to encoded multipart form data

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Some (3) WPT tests were failing because they expected the body for a multipart form data response to end with a CRLF. So I updated encode_multipart_form_data to add the missing terminator.

Looking at the corresponding spec (https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#multipart%2Fform-data-encoding-algorithm) and RFC (https://tools.ietf.org/html/rfc7578), I couldn't find anything mentioned about this detail.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [x] There are tests for these changes

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components/script/dom/htmlformelement.rs

@@ -1366,7 +1366,7 @@ pub fn encode_multipart_form_data(
         }
     }
 
-    let mut boundary_bytes = format!("\r\n--{}--", boundary).into_bytes();
+    let mut boundary_bytes = format!("\r\n--{}--\r\n", boundary).into_bytes();
     result.append(&mut boundary_bytes);
 
     result