KT-45777: Don't include classpath snapshot dir in task output backup

for performance reasons: (1) the snapshots are too big, and (2) they are
usually updated only at the end of the task execution--in a failed task
run, they are usually unchanged and therefore don't need to be restored.

build-common/src/org/jetbrains/kotlin/incremental/fileUtils.kt

@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.incremental
 
 import java.io.File
+import java.io.IOException
 
 fun File.isJavaFile() =
         extension.equals("java", ignoreCase = true)
@@ -26,3 +27,43 @@ fun File.isKotlinFile(sourceFilesExtensions: List<String>): Boolean =
 
 fun File.isClassFile(): Boolean =
         extension.equals("class", ignoreCase = true)
+
+/**
+ * Deletes the contents of this directory (not the directory itself) if it exists, or creates the directory if it does not yet exist.
+ *
+ * If this is a regular file, this method will throw an exception.
+ */
+fun File.cleanDirectoryContents() {
+    when {
+        isDirectory -> listFiles()!!.forEach { it.forceDeleteRecursively() }
+        isFile -> error("File.cleanDirectoryContents does not accept a regular file: $path")
+        else -> forceMkdirs()
+    }
+}
+
+/** Deletes this file or directory recursively (if it exists). */
+fun File.forceDeleteRecursively() {
+    if (!deleteRecursively()) {
+        throw IOException("Could not delete '$path'")
+    }
+}
+
+/**
+ * Creates this directory (if it does not yet exist).
+ *
+ * If this is a regular file, this method will throw an exception.
+ */
+@Suppress("SpellCheckingInspection")
+fun File.forceMkdirs() {
+    when {
+        this.isDirectory -> { /* Do nothing */ }
+        this.isFile -> error("File.forceMkdirs does not accept a regular file: $path")
+        else -> {
+            // Note that if the directory already exists, mkdirs() will return `false`, but here we ensure that the directory does not exist
+            // before calling mkdirs(), so it's safe to check the returned result of mkdirs() below.
+            if (!mkdirs()) {
+                throw IOException("Could not create directory '$path'")
+            }
+        }
+    }
+}