Fix ComboBox text clipping in NET11 VisualStylesMode

[LeafShi1]

• Fixes Text can get truncated in Combobox control in NET11 VisualStylesMode #14794

Root Cause

NET11 modern ComboBox layout reduced the native EDIT child height by vertical padding/chrome. For single-line EDIT, shrinking the window height can clip the text.

Proposed changes

• Preserve the native single-line EDIT child height in modern ComboBox layout.
• Keep bottom-boundary clamping so the EDIT child stays within the modern field.
• Add regression coverage for DropDown and Simple editable ComboBox styles.

Customer Impact

• In VisualStylesMode.Net11 mode, user-entered text is fully displayed, whether at design time or at runtime.

Regression?

• No

Risk

• Minimal

Screenshots

Before

Editable ComboBox text could be vertically clipped.

After

The EDIT child keeps its native height and is only clamped to the available control bounds, so text is no longer clipped under normal sizing.

AfterChanges.mp4

Test methodology

• Unit test and manually

Test environment(s)

• .net 11.0.0-rc.1.26410.101

Microsoft Reviewers: Open in CodeFlow