CLI: improve path relativization for compiler messages

On Windows, the absolute file for the root of the drive is `"C:\"`,
which differs from the absolute file for any other directory, which
doesn't end with `\`. This resulted in incorrect trimming of the first
character of the path name in `descendantRelativeTo`.

Also, do not use canonicalPath because there is no point in expanding
symbolic links here.

 #KT-40979 Fixed

compiler/util/src/org/jetbrains/kotlin/utils/fileUtils.kt

@@ -37,14 +37,9 @@ fun File.withReplacedExtensionOrNull(oldExt: String, newExt: String): File? {
  * If this file does not belong to the [base] directory, it is returned unchanged.
  */
 fun File.descendantRelativeTo(base: File): File {
-    val prefix = base.canonicalPath
-    val answer = this.canonicalPath
-    return if (answer.startsWith(prefix)) {
-        val prefixSize = prefix.length
-        if (answer.length > prefixSize) {
-            File(answer.substring(prefixSize + 1))
-        } else File("")
-    } else {
-        this
-    }
-}
+    assert(base.isAbsolute) { "$base" }
+    assert(base.isDirectory) { "$base" }
+    val cwd = base.normalize()
+    val filePath = this.absoluteFile.normalize()
+    return if (filePath.startsWith(cwd)) filePath.relativeTo(cwd) else this
+}