* `tree` function now accepts the old root rather than the old
`UrlTree`. The `urlTree` argument was only used to get the `root`.
This change makes it more clear what that pararmeter is used for and
what's actually being used
* Move the `oldRoot` (previously `urlTree`) to be the first argument of `tree`.
This change now mirrors the argument order for `replaceSegment` and
can be read from left to right more easily "in this root,
replace this old segment group with this new segment group".
* Extract `newRoot` to a variable. This just makes it more clear what's
going on at the end rather than combining a bunch of operations into
one.
These changes are being made so that hopefully a future refactor can be
done which does not rely on the `urlTree` argument at all in the
`createUrlTree` function. These refactorings will make it easier to see
1:1 functionlity in these various places.
PR Close#45306
a08ea3f643