Fixing constraints.precedingScrollExtent passed to SliverPadding child

[Piinks]

Description

The SliverConstraints passed by RenderSliverEdgeInsetsPadding to its child aren't updating precedingScrollExtent any beforePadding. This becomes apparent when the precedingScrollExtent is used by the child in its layout path, like in the example provided in #49195, and also SliverFillRemaining. This PR fixes that and adds a regression test.

Related Issues

Fixes #49195

Tests

I added the following tests:

SliverPadding updates precedingScrollExtent with beforePadding.

Checklist

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• All existing and new tests are passing.
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Breaking Change

Did any tests fail when you ran them? Please read Handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.

[spkersten]

Thanks for fixing this (and writing the tests)!

[goderbauer]

LGTM

[fluttergithubbot]

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