Added support for an alternative current dir mode in pkldoc (#824)

Some systems have trouble with handling symlinks, which breaks the current directory links created by Pkldoc. In this PR, we add an alternative mode which creates a full copy of the latest published version contents in the current directory instead.

Co-authored-by: Dan Chao <dan.chao@apple.com>

pkl-commons/src/main/kotlin/org/pkl/commons/Paths.kt

@@ -20,6 +20,9 @@ import java.nio.charset.Charset
 import java.nio.file.*
 import java.nio.file.attribute.FileAttribute
 import java.util.stream.Stream
+import kotlin.io.path.copyTo
+import kotlin.io.path.createParentDirectories
+import kotlin.io.path.exists
 
 // not stored to avoid build-time initialization by native-image
 val currentWorkingDir: Path
@@ -51,6 +54,19 @@ fun Path.writeString(
 @Throws(IOException::class)
 fun Path.readString(charset: Charset = Charsets.UTF_8): String = Files.readString(this, charset)
 
+@Throws(IOException::class)
+fun Path.copyRecursively(target: Path) {
+  if (exists()) {
+    target.createParentDirectories()
+    walk().use { paths ->
+      paths.forEach { src ->
+        val dst = target.resolve(this@copyRecursively.relativize(src))
+        src.copyTo(dst, overwrite = true)
+      }
+    }
+  }
+}
+
 private val isWindows by lazy { System.getProperty("os.name").contains("Windows") }
 
 /** Copy implementation from IoUtils.toNormalizedPathString */