[zrt2399]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

• NumberBox sets the arrow cursor on the control through its default
  style. While the underlying TextBox has mouse capture during a click
  or text selection, the cursor is resolved from the control itself, so
  the IBeam cursor is replaced by the default arrow until the mouse
  button is released.
• TextBox sets the IBeam cursor on the control, so the margins around
  the left/right icons and the clear button also show the IBeam cursor
  even though they are not part of the editable area.

What is the new behavior?

Fixes: #1770

• NumberBox sets Cursor to IBeam/Arrow on the templated control
  based on IsEnabled, so the IBeam cursor is preserved while clicking
  and selecting text.
• The arrow cursor is scoped to the left/right icon areas and the
  clear/spin button panel of NumberBox.
• The TextBox icon presenters and clear button are wrapped in
  transparent grids using the arrow cursor, so icon and button margins no
  longer show the IBeam cursor.
• Non-editable areas show the arrow cursor, and the disabled state still
  shows the arrow cursor everywhere.

Other information

XAML-only change, no public API changes.