Ensure the directory exists before writing a file

Summary:
This fixes experimental project generation for IntelliJ on Windows by
ensuring that we've actually created the destination folder prior to
writing out the temporary file to it.

Test Plan:
`buck project --experimental-ij-generation` in
https://github.com/sdwilsh/xplat-buck-demo

Author: sdwilsh

src/com/facebook/buck/java/intellij/IjProjectWriter.java

@@ -147,6 +147,7 @@ protected void writeToFile(ST contents, Path path) throws IOException {
       try (OutputStream outputStream = projectFilesystem.newFileOutputStream(tempFile)) {
         outputStream.write(contents.render().getBytes());
       }
+      projectFilesystem.createParentDirs(path);
       projectFilesystem.move(tempFile, path, StandardCopyOption.REPLACE_EXISTING);
       danglingTempFile = false;
     } finally {