ESR115: decide userAgent rv version

When TB desktop moves to ESR115 it will enter the 110's: see Bugs 1806675,1805967

So before ESR115 lands, decide if we want RFP to respect the freeze rv for compat reasons. Upstream ticket is 1818889 - there is no gain in entropy as all desktops would report rv109 and the real version (in TB's case 115) elsewhere. RFP does not spoof the version on desktop

Android will also move to a hardcoded 115 next ESR cycle. Again, you can do the same, and again no entropy gained. The only difference is that the RFP spoofs the real version for the ESR cycle, so always 109/115

Otherwise, it's a year until the next ESR