Prepare for upgrade to java-diff-utils 4.12

The new version of the library doesn't have a `DiffException` that the
current version forces us to catch. We cannot upgrade to the library and
change the code that uses it in the same change for complicated reasons,
so instead catch `Exception` to remove the use of a soon-to-be-eliminated
class.

PiperOrigin-RevId: 567365082

Author: brad4d

src/com/google/javascript/rhino/testing/TextDiffFactsBuilder.java

@@ -45,7 +45,6 @@
 
 import com.github.difflib.DiffUtils;
 import com.github.difflib.UnifiedDiffUtils;
-import com.github.difflib.algorithm.DiffException;
 import com.github.difflib.patch.Patch;
 import com.google.common.base.Splitter;
 import com.google.common.collect.ImmutableList;
@@ -92,7 +91,8 @@ public ImmutableList<Fact> build() {
           UnifiedDiffUtils.generateUnifiedDiff(
               "expected", "actual", expectedLines, patch, /* contextSize= */ 10);
       return ImmutableList.of(fact(title, unifiedDiff.stream().collect(joining("\n"))));
-    } catch (DiffException e) {
+    } catch (Exception e) {
+      // TODO: b/238438892 - Remove the try/catch entirely after upgrading to java-diff-utils 4.12
       // It's unclear when this exception happens.
       // It may indicate a bug in the diff library itself.
       throw new IllegalStateException(e);