Fix detailed-diff highlight clipping at end of trimmed diff string

[tobiasmelcher]

When a detailed diff ended exactly at the last character of the trimmed diff string (start + length == trimmedLength), the old >= guard reduced the highlight length by the number of stripped trailing newlines, cutting off that many characters from the highlight rectangle. The condition is now >, so the length is only clamped when the range actually overshoots.

The same bug existed independently in computeDetailedDiffRanges and createDetailedDiffBackgroundRanges; both now delegate to a shared helper clampDetailedDiffLength in UnifiedDiffText.

Additionally, in getPositionForOffset a newline at the very start of a style range (lfIdx == 0) was ignored, so the x offset was not reset and the following text was mispositioned. The guard is now lfIdx >= 0.

Reviewed with the help of Claude Code.

[tobiasmelcher]

Screenshot from ABAP Development Tools in Eclipse showing the defect: on the added "percentWarning": 1.2, line the green highlight is clipped and stops short of the line end, instead of covering the full changed text like the other added lines.

[github-actions]

Test Results

    54 files  ± 0      54 suites  ±0   59m 15s ⏱️ + 2m 26s
 4 828 tests + 5   4 806 ✅ + 5   22 💤 ±0  0 ❌ ±0 
12 375 runs  +15  12 222 ✅ +15  153 💤 ±0  0 ❌ ±0 

Results for commit 0cd742c. ± Comparison against base commit a439595.

♻️ This comment has been updated with latest results.

[BeckerWdf]

Screenshot from ABAP Development Tools in Eclipse showing the defect: on the added "percentWarning": 1.2, line the green highlight is clipped and stops short of the line end, instead of covering the full changed text like the other added lines.

so the marked boxes should be more left and be the background of the "1.2" text.