Fix mimeType parsing for CDP responses (#53027)

Summary:
Pull Request resolved: #53027

Tweaks MIME type parsing in CDP Network messages, now matching Chrome.

This fixes response preview behaviour by the frontend for text response previews that are `base64Encoded` 🙌🏻 (we were observing these for JSON `fetch` calls on iOS).

Changelog: [Internal]

Reviewed By: vzaidman

Differential Revision: D79559495

fbshipit-source-id: 2565af7587fc6fbdd3ef6fcbb10c558341ddfbdc

Author: huntie

packages/react-native/ReactCommon/jsinspector-modern/network/HttpUtils.cpp

@@ -154,7 +154,15 @@ std::string mimeTypeFromHeaders(const Headers& headers) {
     std::transform(
         lowerName.begin(), lowerName.end(), lowerName.begin(), ::tolower);
     if (lowerName == "content-type") {
-      mimeType = value;
+      // Parse MIME type (discarding any parameters after ";") from the
+      // Content-Type header
+      // https://datatracker.ietf.org/doc/html/rfc7231#section-3.1.1.1
+      size_t pos = value.find(';');
+      if (pos != std::string::npos) {
+        mimeType = value.substr(0, pos);
+      } else {
+        mimeType = value;
+      }
       break;
     }
   }