Drop support for versions lower than Gradle 8.0

[Omico]

Since Compose Multiplatform 1.7.1, the minimum AGP version has been raised to 8.1.0. This means the minimum Gradle version is 8.0. Thus, we can safely remove this function.
https://www.jetbrains.com/help/kotlin-multiplatform-dev/whats-new-compose-170.html#minimum-agp-version-raised-to-8-1-0
https://developer.android.com/build/releases/past-releases/agp-8-1-0-release-notes

[Omico]

@terrakok, I need some help. Is this still relevant? This prevents compilation, if we raise the Kotlin language version to 1.8.

compose-multiplatform/gradle-plugins/compose/src/main/kotlin/org/jetbrains/compose/desktop/application/tasks/AbstractJPackageTask.kt

Lines 329 to 344 in e912311

	/**
	* Gradle runtime verification fails,
	* if InputDirectory is not null, but a directory does not exist.
	* The directory might not exist, because prepareAppResources task
	* does not create output directory if there are no resources.
	*
	* To work around this, appResourcesDir is used as a real property,
	* but it is annotated as @Internal, so it ignored during inputs checking.
	* This property is used only for inputs checking.
	* It returns appResourcesDir value if the underlying directory exists.
	*/
	@Suppress("unused")
	@get:InputDirectory
	@get:Optional
	internal val appResourcesDirInputDirHackForVerification: Provider<Directory>
	get() = appResourcesDir.map { it.takeIf { it.asFile.exists() } }

[terrakok]

the minimum AGP version has been raised to 8.1.0. This means the minimum Gradle version is 8.0.

Projects with no android still may use Gradle 7.1