Honor executableDir and applicationName in application extension

[Goooler]

Follow up #1738.

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• CHANGELOG's "Unreleased" section has been updated, if applicable.

[Copilot]

Pull Request Overview

This PR extends the shadow plugin to properly honor the applicationName property from the application extension, building on the previous work to honor executableDir. The changes ensure that when users configure a custom application name, it's consistently used throughout the shadow distribution process.

• Updates distribution configuration to use custom application name in base name
• Refactors provider usage for better consistency with method references
• Adds comprehensive test coverage for both applicationName and executableDir properties

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
ShadowApplicationPlugin.kt	Updates distribution configuration to honor applicationName and refactors provider usage
ApplicationPluginTest.kt	Adds test coverage for applicationName and executableDir extension properties
README.md	Updates changelog to document the new applicationName support

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