Encode filepaths to be safe on Windows

This changes the file paths to use characters that are safe for Windows.

Channges the output of the following:
* Package cache directory
* Generated pkl-doc files
* Kotlin generated code

Unsafe characters are encoded as (<hex>).
For example, the colon character `:` is encoded as `(3a)`.

Additionally, this changes the cache directory prefix (package-1 to
package-2).

Follows the design of https://github.com/apple/pkl-evolution/pull/3

pkl-commons-test/src/main/kotlin/org/pkl/commons/test/PackageServer.kt

@@ -51,7 +51,14 @@ class PackageServer : AutoCloseable {
     const val FRUIT_1_1_SHA = "8d982761d182f2185e4180c82190791d9a60c721cb3393bb2e946fab90131e8c"
 
     fun populateCacheDir(cacheDir: Path) {
-      val basePath = cacheDir.resolve("package-1/localhost:$PORT")
+      doPopulateCacheDir(cacheDir.resolve("package-2/localhost(3a)$PORT"))
+    }
+
+    fun populateLegacyCacheDir(cacheDir: Path) {
+      doPopulateCacheDir(cacheDir.resolve("package-1/localhost:$PORT"))
+    }
+
+    private fun doPopulateCacheDir(basePath: Path) {
       basePath.deleteRecursively()
       Files.walk(packagesDir).use { stream ->
         stream.forEach { source ->