Fix elevationBrushes to match WinUI

[Difegue]

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?

Card controls that use ControlElevationBrush show broken borders, as the gradient remains at the height of regular button/combobox controls.
Conversely, if Card controls are what are shown first, the ElevationBrush will not function properly for ComboBoxes and Buttons.

This also affects textboxes that are larger in height than the normal one. The replacement was to use a different ElevationBrush that does a full gradient, but this is non-canonical relative to WinUI.

I've also noticed that NumberBoxes/PasswordBoxes don't have a correct bottom border - The idea was probably to rely on the additional accent border instead, but that doesn't work as intended.

Issue Number: N/A

What is the new behavior?

• ControlElevationBrush works properly.
• TextElevationBrush has been fixed to match WinUI.
• NumberBox/PasswordBox has been fixed to use the ElevationBrush properly alongside the additional accent border

Other information