LT-22452 - fix mouse scrolling on date field in lex edit

[johnml1135]

JIRA Explanation for LT-22452

Problem:
Mouse wheel scrolling does not work in the Lexicon Editor when the cursor is over the Date field (and potentially other non-ButtonLauncher controls in the DataTree).

Root Cause:
The Date field (DateSlice in BasicTypeSlices.cs) wraps a RichTextBox set to ReadOnly with BorderStyle.None. RichTextBox inherits from ScrollableControl and has internal scroll machinery that consumes WM_MOUSEWHEEL messages without propagating them to the parent DataTree. Win32 delivers WM_MOUSEWHEEL to the focused window handle (the RichTextBox), so the message never reaches DataTree and its AutoScrollPosition property is never updated — the pane doesn't scroll.

This is a general WinForms problem: any child control that internally handles WM_MOUSEWHEEL (e.g. RichTextBox, ListView, TreeView) will swallow the mouse wheel and prevent its container from scrolling.

Fix:
Added a WheelRedirector inner class to DataTree that implements IMessageFilter — a .NET/WinForms mechanism that intercepts Windows messages at the application message pump before they are dispatched to any window. This is the same pattern used in 7 other places in the FieldWorks codebase (e.g. FwFindReplaceDlg, SimpleRootSite, FwApp).

When WM_MOUSEWHEEL is intercepted, the filter checks whether the cursor is over any live DataTree instance. If so, it calculates the new scroll position using the same AutoScrollPosition/AutoScrollMinSize API that DataTree itself uses, applies it, and marks the message as handled. This ensures consistent scrolling regardless of which child control has focus.

Changes:

• DataTree.cs: Added WheelRedirector inner class (~65 lines), Register() call in constructor, Unregister() call in Dispose.
• DataTreeScrollTests.cs: New test verifying the scroll position calculation works correctly.
• No changes to ButtonLauncher.cs or any other file.

Made changes.

---

This change is 

[github-actions]

NUnit Tests

    1 files      1 suites   6m 6s ⏱️
4 408 tests 4 321 ✅ 87 💤 0 ❌
4 417 runs  4 330 ✅ 87 💤 0 ❌

Results for commit ba633e1.

[jasonleenaylor]

It looks like this test adds another test that pops up a window while it is running. I was hoping to get away from that, I'd rather not have a unit test for this if that is the case.

@jasonleenaylor reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: 1 of 3 files reviewed, all discussions resolved.