[Compare] Show move-button marker for larger diffs with range connection

When comparing diffs with five or more lines, show the 'move'-button
markers even when using range connections in order to assist the user in
finding the move buttons, which only appear when hovering over them.
For smaller diffs the marker is not shown to clutter the UI less as the
markers are then relatively easy to find in the middle of the range.

Follow-up on
- #2565

Author: HannesWell

team/bundles/org.eclipse.compare/compare/org/eclipse/compare/contentmergeviewer/TextMergeViewer.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2025 IBM Corporation and others.
+ * Copyright (c) 2000, 2026 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -4522,11 +4522,13 @@ private void paintCenter(Canvas canvas, GC g) {
 
 				fLeft.getLineRange(diff.getPosition(LEFT_CONTRIBUTOR), region);
 				region.x -= fLeft.getDocumentRegionOffset();
+				int diffLines = region.y;
 				int ly = getHeightBetweenLines(fLeft, 0, region.x) + lshift;
 				int lh = getHeightBetweenLines(fLeft, region.x, region.x + region.y);
 
 				fRight.getLineRange(diff.getPosition(RIGHT_CONTRIBUTOR), region);
 				region.x -= fRight.getDocumentRegionOffset();
+				diffLines = Math.max(diffLines, region.y);
 				int ry = getHeightBetweenLines(fRight, 0, region.x) + rshift;
 				int rh = getHeightBetweenLines(fRight, region.x, region.x + region.y);
 
@@ -4579,7 +4581,7 @@ private void paintCenter(Canvas canvas, GC g) {
 					}
 				}
 
-				if (fUseSingleLine && isAnySideEditable()) {
+				if ((fUseSingleLine || diffLines >= 5) && isAnySideEditable()) {
 					// draw resolve state
 					int cx= (w-RESOLVE_SIZE)/2;
 					int cy= ((ly+lh/2) + (ry+rh/2) - RESOLVE_SIZE)/2;