Remove deprecated mainContentSlivers field in SliverWoltModalSheetPage

[ulusoyca]

Description

Removes the previously marked as deprecated mainContentSlivers in favor of mainContentSliversBuilder field.

Before

SliverWoltModalSheetPage(
  mainContentSlivers: [
    SliverList(
      delegate: SliverChildBuilderDelegate((BuildContext context, int index) {
        // Your list items
      }),
    ),
    // Other sliver widgets...
  ],
  // Additional page elements like pageTitle, topBarTitle, etc.
)

After

SliverWoltModalSheetPage(
  mainContentSliversBuilder: (context) => [
    SliverList(
      delegate: SliverChildBuilderDelegate((BuildContext context, int index) {
        // Your list items
      }),
    ),
    // Other sliver widgets...
  ],
  // Additional page elements like pageTitle, topBarTitle, etc.
)

Related Issues

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• [x] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] My PR includes tests for all changed/updated/fixed behaviors.
• [x] All existing and new tests are passing.
• [x] I updated/added relevant documentation (doc comments with ///).
• [x] The analyzer (melos run analyze) does not report any problems on my PR.
• [x] The package compiles with the minimum Flutter version stated in the pubspec.yaml

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• [x] Yes, this is a breaking change.
• [ ] No, this is not a breaking change.