feat: include error as description for parse errors closes

[MasterOdin]

Note: the socket.io.js file is the generated output of make socket.io.js, and should not be manually modified.

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behaviour

When the client has an error decoding incoming data, it will currently close current connection, which will retrigger a reconnect. However, there's no good way to know what might have caused the parse error and makes debugging them much harder.

New behaviour

Now, the error that was raised during parsing is attached as the optional description field on the onclose and so the user can get at it as described in the 4.5.0 release notes.

The error includes the data for ease of debugging, but that could probably be removed as that info should be accessible via the network inspection.

Other information (e.g. related issues)

Closes #1554

[darrachequesne]

Merged into 2403b88. Thanks a lot 👍