fix: A bug fix

[MultiX0]

fix: Resolve unresolved reference errors in Workmanager plugin

This PR fixes compilation errors in the workmanager package that caused unresolved references to shim, ShimPluginRegistry, PluginRegistrantCallback, and Registrar in BackgroundWorker.kt and WorkmanagerPlugin.kt.

The issue was preventing the project from building successfully, specifically failing at :workmanager:compileDebugKotlin.

Updated references to align with the latest Flutter embedding changes.
Ensured compatibility with newer versions of Kotlin and Flutter.

[docs-page[bot]]

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[ened]

Closing this PR as it has been superseded by the comprehensive modernization work in v0.7.0 (PR #610). The version 0.7.0 includes updated Android Gradle Plugin 8.10.1, Kotlin 2.1.0, SDK 35, and all the latest toolchain updates that address the build issues this PR was attempting to fix.