LT-22688: Arrow keys move between writing systems

[aror92]

Fix Avalonia tab traversal in multistring fields. Rather than having a tab stop at every writing system of a multistring field and at every paragraph of a structured-text field in Avalonia, use one tab stop per field and move between writing systems with the arrow keys (matching WinForms behavior).

Fix highlighting in reference vector fields. Once focused on, a reference vector field would remain highlighted until another reference vector field was selected. The highlight is painted now only while the field or one of its menus is in focus.

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Update Avalonia behavior to use arrow keys instead of tab stops to move between WSs:
DetailValueStopGroup (new), used by FwMultiWsTextField and FwStructuredTextField: only the first enterable editor is a Tab stop. Up and Down move to the next or previous writing system (or paragraph) from the last or first visual line. Left and Right do the same at the text edges, and an empty value moves at once. Shift+Tab from a later editor leaves the field. Tab entry puts the caret at the start of existing text instead of selecting all of it.

FwMultiWsTextField's navKeyDown handles every Left/Right press itself, so it now asks the group first; relying on handler order left the edge crossing unreachable in editable rows.

Fix ReferenceVectorField highlighting:
FwReferenceVectorField: the current item stayed highlighted after focus moved on, until another vector row selected an item. The highlight is now painted only while focus is inside the field, a menu gesture is in progress, or one of the item's own menus is open. The item still stays current for menus.

DetailMenuRequest: BeginMenuGesture and EndMenuGesture now reach the row's selection source even without a text editor, so a read-only item stays highlighted while its right-click menu is open.

Add tests:
DataTreeTabNavigationIntegrationTests.cs: replaced the test that expected Tab to visit every writing system, and added tests for Up/Down, Left/Right, Shift+Tab, structured-text paragraphs and caret placement. DetailMenuTests.cs: added the highlight tests.

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This change is 

[github-actions]

NUnit Tests

    1 files      1 suites   13m 45s ⏱️
6 656 tests 6 571 ✅ 85 💤 0 ❌
6 665 runs  6 580 ✅ 85 💤 0 ❌

Results for commit 1e0d9b3.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.98131% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.62%. Comparing base (2b981ed) to head (1e0d9b3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/Common/FwAvalonia/Detail/DetailValueStopGroup.cs	80.14%	7 Missing and 21 partials ⚠️
Src/Common/FwAvalonia/Detail/DetailModel.cs	77.77%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           main    #1181       +/-   ##
=========================================
+ Coverage      0   39.62%   +39.62%     
=========================================
  Files         0     1541     +1541     
  Lines         0   354887   +354887     
  Branches      0    41175    +41175     
=========================================
+ Hits          0   140616   +140616     
- Misses        0   184880   +184880     
- Partials      0    29391    +29391     

Files with missing lines	Coverage Δ
Src/Common/FwAvalonia/Detail/FwFieldControls.cs	87.56% <100.00%> (ø)
.../Common/FwAvalonia/Detail/FwStructuredTextField.cs	79.86% <100.00%> (ø)
Src/Common/FwAvalonia/Detail/DetailModel.cs	78.84% <77.77%> (ø)
...c/Common/FwAvalonia/Detail/DetailValueStopGroup.cs	80.14% <80.14%> (ø)

... and 1537 files with indirect coverage changes

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[github-actions]

Comment hygiene (advisory)

No comment-style violations in the lines this branch adds since origin/main.

[thejambi]

Src/Common/FwAvalonia/Detail/DetailValueStopGroup.cs line 208 at r1 (raw file):

		// True when the caret sits on the first (or last) visual line of a wrapped editor, so the
		// arrow has nowhere left to go inside it. An editor with no laid-out text is one line.
		private static bool IsOnEdgeLine(TextBox box, bool first)

Suggestion: add a test for Up/Down in text that wraps

IsOnEdgeLine and CaretNearX are the most layout-sensitive parts of this change. They decide whether Up/Down stays inside a wrapped value or moves to the next writing system, and where the caret lands when it moves. All the Up/Down tests use short single-line values, so neither branch runs; that's where most of this file's partially covered lines in Codecov come from.

One test would cover both. Use a narrow window and a value long enough to wrap to three lines, then check:

1. With the caret on line 1, Down keeps focus in the same box and moves the caret down a line.
2. With the caret on line 3, Down moves focus to the next writing system, and the caret lands near the same horizontal position.
3. Optionally, the mirror case: with the caret on line 1 of a later writing system, Up moves to the previous one.

Not blocking. The single-line behavior is well covered, and this would protect the wrapped case against layout changes.

[thejambi]

@thejambi reviewed 7 files and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on aror92).

[thejambi]

@thejambi reviewed 3 files and all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on aror92).