[ZEPPELIN-6584] Fix reversed line diff direction in New UI revision comparator

[JangAyeon]

What is this PR for?

The New UI revision comparator labels a comparison as first --> second (e.g. older --> newer), but compareRevisions() built the line-level diff from the second revision back to the first. As a result, added lines were rendered as red deletions and removed lines as green insertions for paragraphs present in both revisions.

This PR computes the line diff in the same first --> second direction shown in the UI, matching the legacy AngularJS comparator (diffLines(firstText, secondText)). The whole-paragraph added/deleted classification, which was already correct, is unchanged.

What type of PR is it?

Bug Fix

Todos

• - Fix line diff direction
• - Add focused comparator unit tests

What is the Jira issue?

ZEPPELIN-6584

How should this be tested?

• Unit tests:

  cd zeppelin-web-angular
  npm run test:shell -- revisions-comparator.component.spec.ts
  npm run lint

Screenshots (if appropriate)

Questions:

• Does the license files need to update? No
• Is there breaking changes for older versions? No
• Does this needs documentation? No

[jongyoul]

Reviewed fa674b0. The first/from -> second/to direction now matches the selectors and insert/delete rendering, while whole-paragraph classification is preserved. The five focused comparator tests passed in both exact-head CI jobs; an isolated exact-source probe also distinguished the fix from the reversed-direction baseline. No actionable issue found in this bounded change.

CI is not fully green: the auth keyboard E2E failed while waiting on PENDING, the anonymous classic phase was cancelled, and Selenium setup hit a Maven Central download timeout. This is a code-review approval, not confirmation that all merge checks have passed.

[voidmatcha]

Merged into master (45f305a).