[MacOS] Fix inconsistent response to custom height across controls

[apman]

This fixes a number of inconsistencies across MacOS controls in how they respond to explicit height settings.

Before: some controls did not respond at all, some grew to the set size but lost their margins, potentially leading to focus highlight being cut off, some grew overall to the requested size leaving room for the margins (so the visible size is 3px less)

After: I have now taken the latter approach for all controls.

While it might seem slightly confusing that a "30px" control has a visible height of 27px, it guarantees that the control is self-contained and won't visually bleed over other controls or get clipped unexpectedly.

Consumers will need to account for the margin (e.g. set Height="33" to achieve 30 for the unfocussed visual appearance), or don't set a height at all and let the theme dictate the natural size (which is usually the best practice).

[Copilot]

Pull request overview

This PR addresses inconsistent behavior across MacOS controls when custom heights are set. The fix ensures all controls grow to the requested size while reserving 3px margins for focus highlights, preventing visual clipping or bleeding. The approach standardizes the behavior so controls maintain self-contained rendering with proper focus border spacing.

Key changes:

• Removed explicit height bindings from internal border elements in TextBox and TagInput controls
• Changed margin resource references from StaticResource to DynamicResource for consistency
• Added explicit height binding to NumericUpDown's inner TextBox
• Updated MultiComboBox horizontal alignment to Stretch for better layout behavior

Reviewed changes

Copilot reviewed 16 out of 26 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
TextBox.axaml	Removed Height bindings from internal borders and changed margin to DynamicResource
TagInput.axaml	Removed Height binding from border and updated margin resource reference
RadioButton.axaml	Changed margin resource reference to DynamicResource
NumericUpDown.axaml	Added Height binding to PART_TextBox for consistency
MultiComboBox.axaml	Changed HorizontalAlignment to Stretch and margin to DynamicResource
Devolutions.AvaloniaTheme.MacOS.csproj	Updated release notes and cleaned up XML formatting
Visual test baselines	Updated PNG screenshots to reflect new control rendering behavior

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