Move Proguard version from ProguardSettings.kt To Gradle version catalog

[ellet0]

This change is specific to Compose Desktop, when using Compose Desktop Gradle plugin to build the release version of the application

Move the Proguard version from ProguardSettings.kt to gradle/libs.versions.toml without any breaking change, this PR shouldn't affect the functionality, tests, or anything in any way

Testing

Describe how you tested your changes. If possible and needed:

• Test it on a sample project: The examples use the libraries and plugins of Compose Desktop from Maven Central, I couldn't test this change on the new blank project as the Gradel build took longer than usual (about 1H), gradlew build -x test didn't skip the tests, in general, this PR should not introduce any new bugs, the property DEFAULT_PROGUARD_VERSION was is private in ProguardSettings.kt
• Write unit tests: I couldn't find ComposeBuildConfigTest or anything that tests the generated file, DEFAULT_PROGUARD_VERSION, or anything that's related to adding new tests.
• Provide a code snippet: This doesn't change how the developers will use the project, the goal is to help maintain the repository, Some versions are in gradle.properties others are in gradle/libs.versions.toml, I wasn't certain when should I use the Gradel version catalog or gradle.properties in this project

Let me know if any additional changes are required or if I should move the Proguard version to gradle.properties, rename the default-proguard