Randomize temporary sketch copy directory name

When a sketch has unsaved changes, a temporary copy of the sketch is
made with those changes applied. This copy is then passed to
arduino-builder.

Previously, the name of this directory contained a hash of the main
sketch filename, so the same directory would be used between builds. Now
that this directory is deleted after every build, it can just use a
randomized directory name, which is what this commit does.

Addtionally, the prefix used for generating the name is changed from
"arduino_" to "arduino_modified_sketch_" to make it slightly clearer
what the directory is for (just in case it somehow survives the build,
or a user sees it during the build).

Author: matthijskooijman

app/src/processing/app/Sketch.java

@@ -1119,7 +1119,7 @@ private String build(String buildPath, boolean verbose, boolean save) throws Run
   }
 
   private String saveSketchInTempFolder() throws IOException {
-    File tempFolder = FileUtils.createTempFolder("arduino_", DigestUtils.md5Hex(data.getMainFilePath()));
+    File tempFolder = FileUtils.createTempFolder("arduino_modified_sketch_");
     FileUtils.copy(getFolder(), tempFolder);
 
     for (SketchCode sc : Stream.of(data.getCodes()).filter(SketchCode::isModified).collect(Collectors.toList())) {