Rewrite M2TS packet output

Rewrite M2TS packet output

Make sure we only write the bottom 30 bits of the PCR to the m2ts header.
Don't use floating point computation for it, and remove weird bit fiddling
that messes up the PCR in a way I can't find any
justification/documentation for.

Don't accidentally lose PCR packets from the output.

Fix the description for the m2ts-mode property so it's clear it's a flag,
and which setting does what.

Fixes: #611061 #644429
Partially fixes: #645006