In order to follow spec text to achieve this, we need to change the
underlying representation of a host in AK::URL to deserialized format.
Before this, we were parsing the host and then immediately serializing
it again.
Making that change resulted in a whole bunch of fallout.
After this change, callers can access the serialized data through
this concept-host-serializer. The functional end result of this
change is that IPv6 hosts are now correctly serialized to be
surrounded with '[' and ']'.
This patch replaces the usage of QPalette::PlaceholderText with
QPalette::Text with opacity reduced to roughly 50%. This fixes the non
highlighted spans having an extremely low contrast compared to the
background in dark mode.
