FormFilter does not adjust Content-Length header #3972
Description
Describe the bug
FormFilter can recreate produce body bigger than original but Content-Length header is not changed.
Any other processing may fail because it may read body up to Content-Length trimming it in the process.
Sample
Example is exlamation mark character.
When sending x-www-form-urlencoded form a browser it will not encode "!" into %21.
It will count this character as 1 byte
However FormFilter will encode the character here increasing the output by 2 bytes