Editorial: reform some navigation parameters

This introduces explicit optional parameters for the navigation
algorithm, exceptionsEnabled and replacementEnabled. It then takes care
to thread these through to all call sites explicitly; replacementEnabled
in particular is consulted all over the place. Previously, these were
passed and consulted in an ad-hoc manner, often involving deeply-nested
calls talking about "the value that the navigation algorithm was
originally invoked with".

Along the way, this cleans up several calling algorithms, including
Location-object navigate, Location-object setter navigate, and frame and
iframe processing. They are now generally more explicit, and the
frame/iframe element processing contains less duplicated spec text.

This sets the stage for making other currently-implicit inputs to the
navigation algorithm into explicit, but optional, parameters. For
example, navigation type ("form-submission" or "other"),
"reload-triggered navigation", and "entry update". That will be done in
future commits.

Closes #5757.