Update Checkstyle integration test (#1424)

Summary of changes:
- Move Checkstyle-specific build parameters out of
  `run-integration-test.sh`.
- Build with `-Dmaven.compiler.failOnError=true` to compensate for
  `<failOnError>false</failOnError>` configured by the enabled Maven
  profiles.
- Tweak `XdocGenerator.java` logic prior to integration test execution,
  to work around a subtle semantic difference introduced by the
  `FilesCreateTempFileToFile` Refaster rule.
- Document this difference on the relevant Refaster rules.
- To aid debugging, run Maven commands with `set -x`, such that the
  exact command executed is logged.
- Update the patch file containing the expected changes.

error-prone-contrib/src/main/java/tech/picnic/errorprone/refasterrules/FileRules.java

@@ -93,6 +93,12 @@ String after(Path path) throws IOException {
   /**
    * Prefer {@link Files#createTempFile(String, String, FileAttribute[])} over alternatives that
    * create files with more liberal permissions.
+   *
+   * <p>Note that {@link File#createTempFile} treats the given prefix as a path, and ignores all but
+   * its file name. That is, the actual prefix used is derived from all characters following the
+   * final file separator (if any). This is not the case with {@link Files#createTempFile}, which
+   * will instead throw an {@link IllegalArgumentException} if the prefix contains any file
+   * separators.
    */
   static final class FilesCreateTempFileToFile {
     @BeforeTemplate
@@ -117,6 +123,12 @@ File after(String prefix, String suffix) throws IOException {
   /**
    * Prefer {@link Files#createTempFile(Path, String, String, FileAttribute[])} over alternatives
    * that create files with more liberal permissions.
+   *
+   * <p>Note that {@link File#createTempFile} treats the given prefix as a path, and ignores all but
+   * its file name. That is, the actual prefix used is derived from all characters following the
+   * final file separator (if any). This is not the case with {@link Files#createTempFile}, which
+   * will instead throw an {@link IllegalArgumentException} if the prefix contains any file
+   * separators.
    */
   static final class FilesCreateTempFileInCustomDirectoryToFile {
     @BeforeTemplate