compat: align userAgent in navigator + HTTP Header

links

• upstream 1918009
• test: https://canvasblocker.kkapsner.de/test/navigatorTest.php

there is no entropy gained, as we already limit the strings in navigator. this should simplify things as well, and maybe we can remove an RFPTarget (never really understood why we have two). So while we removed a red flag of mismatching OSes in HTTP Headers, we still break the spec and leave a red flag to target us

RFP on (windows)

user agent equal between server and client: false

server site user agent: Mozilla/5.0 (Windows NT 10.0; rv:128.0) Gecko/20100101 Firefox/128.0
             userAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0

RFP off

user agent equal between server and client: true

server site user agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0
             userAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:128.0) Gecko/20100101 Firefox/128.0

ToDo: check on android @dan , linux @pierov , mac

We should get this into 14 before it hits stable @morgan and maybe cloudflare needs an update