carousel: Support add/remove animations for indicators

Since these animations are time-based and the duration is known, it's
enough to just have a tick callback triggering redraws for the indicator
widget on each frame until the time runs out.

Signed-off-by: Alexander Mikhaylenko <alexm@gnome.org>
11 jobs for wip/exalm/paginator-animate in 21 minutes and 2 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
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passed build-debian-clang #738567

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flatpak

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flatpak

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  Package
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  Test Package
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passed lintian-debian-buster-package #738575

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