Appends something like `name="value"` to string, taking care to escape any quotes or backslashes in value.
If value is (non-ASCII) UTF-8, this will instead use RFC 5987 encoding, just like [func@header_g_string_append_param].
| string |
a StringBuilder being used to construct an HTTP header value |
| name |
a parameter name |
| value |
a parameter value |