[ReplacedNG] Switch flexbox to use NGReplacedLayoutAlgorithm

Previously we had bespoke logic for this part. This switches the logic
to use the ComputeReplacedSize function and kIgnoreBlockLengths,
kIgnoreInlineLengths parameters.

Bug: 1114280
Change-Id: Id4726b79c755f25f86b5dc4513e312191498db7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2837072


Reviewed-by: David Grogan <dgrogan@chromium.org>
Commit-Queue: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#908699}