[Gradle] Fix switching in-process to Native embeddable compiler jar

Compiler runner used incorrect cache key for isolated classloader:
it didn't take the actually used compiler jar into account,
only the K/N home dir.

Fix this by using the entire classpath as a key.

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/native/NativeEmbeddableCompilerJarIT.kt

@@ -55,4 +55,25 @@ class NativeEmbeddableCompilerJarIT : BaseGradleIT() {
             }
         }
     }
+
+    @Test
+    fun testSwitch() = with(transformNativeTestProjectWithPluginDsl("executables", directoryPrefix = "native-binaries")) {
+        build(":runDebugExecutableHost") {
+            assertSuccessful()
+            checkNativeCompilerClasspath(":linkDebugExecutableHost", ":compileKotlinHost") {
+                assertTrue(it.includesRegularJar())
+                assertFalse(it.includesEmbeddableJar())
+            }
+        }
+
+        build(":clean") {} // Ensure the tasks aren't up-to-date.
+
+        build(":runDebugExecutableHost", "-Pkotlin.native.useEmbeddableCompilerJar=true") {
+            assertSuccessful()
+            checkNativeCompilerClasspath(":linkDebugExecutableHost", ":compileKotlinHost") {
+                assertFalse(it.includesRegularJar())
+                assertTrue(it.includesEmbeddableJar())
+            }
+        }
+    }
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/compilerRunner/nativeToolRunners.kt

@@ -99,7 +99,10 @@ internal abstract class KotlinNativeToolRunner(
             """.trimIndent()
         }
 
-    final override val isolatedClassLoaderCacheKey get() = project.konanHome
+    data class IsolatedClassLoaderCacheKey(val classpath: Set<java.io.File>)
+
+    // TODO: can't we use this for other implementations too?
+    final override val isolatedClassLoaderCacheKey get() = IsolatedClassLoaderCacheKey(classpath)
 
     override fun transformArgs(args: List<String>) = listOf(toolName) + args