[KGP] Fix sharing build cache between Windows and Linux

On Windows, path() uses backslash as a file separator, and Mac/Linux
are using forward slashes. If friendPathsSet differs, remote build outputs
from other platforms can't be reused.

This patch uses invariant paths to address the issue.

^KT-63460 Fixed


Merge-request: KT-MR-13261
Merged-by: Evgenii Mazhukin <evgenii.mazhukin@jetbrains.com>

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/tasks/AbstractKotlinCompile.kt

@@ -111,7 +111,7 @@ abstract class AbstractKotlinCompile<T : CommonCompilerArguments> @Inject constr
             val buildDirFile = projectLayout.buildDirectory.asFile.get()
             return friendPaths
                 .filter { it.exists() }
-                .map { it.normalize().relativeTo(buildDirFile).path }.toSet()
+                .map { it.normalize().relativeTo(buildDirFile).invariantSeparatorsPath }.toSet()
         }
 
     @Deprecated("Scheduled for removal with Kotlin 2.0", ReplaceWith("moduleName"))