…anifest (#38639) (#38646)

* don't force leading slash for external redirects

* add test

* perf: regexp -> double String.startWith checks

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Co-authored-by: Michal Piechowiak <misiek.piechowiak@gmail.com>
(cherry picked from commit 5dbcf9e)

Co-authored-by: Jenae Janzen <101715009+jenae-janzen@users.noreply.github.com>

…ge placeholderUrl (#38626) (#38647)

(cherry picked from commit b177db9)

Co-authored-by: Carlos Fernandes Cunha <cunhacf@users.noreply.github.com>

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