Added unit test coverage for VisualStylesMode rendering scenarios in NumericUpDown and Button controls.

[abineshPalanisamy]

Fixes #4212

Proposed changes

• Added rendering tests for NumericUpDown with VisualStylesMode.Net11 and VisualStylesMode.Classic.
• Added rendering tests for Button with VisualStylesMode.Net11 and VisualStylesMode.Classic.
• Added validation for rendering scenarios including normal, read-only, disabled, and FlatStyle configurations.
• Added verification that changing NumericUpDown.VisualStylesMode invalidates the control and triggers layout updates.
• Ensured controls render successfully via DrawToBitmap without exceptions when visual styles are disabled.

Customer Impact

• Improves test coverage for control rendering when visual styles are disabled.
• Helps prevent regressions in rendering behavior across supported VisualStylesMode configurations.

Regression?

• No

Risk

• Low
• Changes are limited to unit test coverage and do not modify product functionality.

Test methodology

• Executed existing WinForms unit test suite.
• Added and executed new rendering tests for NumericUpDown.
• Added and executed new rendering tests for Button.

Test environment(s)

• 11.0.100-preview.6.26359.118

Microsoft Reviewers: Open in CodeFlow