System font scaling not working on the fly

[JayashreeSF3546]

Fixes #3583

Proposed changes

• Updated default font change handling to react when the system/default font changes at runtime.
• Cleared cached default/control font handles before raising OnFontChanged.

Customer Impact

• WinForms apps using inherited/default fonts now refresh more reliably when system text size/font changes.
• Reduces inconsistent UI states where text updates but controls do not visually refresh correctly until restart.

Regression?

• No

Risk

• Low to medium: touches runtime font-change handling, but only for controls using the default/inherited font path.

Screenshots

Before

After

Test methodology

• Verified behavior manually with a WinForms sample using AutoScaleMode.Font.
• Tested runtime increase/decrease of system text size/font and observed control refresh behavior.
• Confirmed explicitly set control fonts are not affected by the default/inherited font update path.

Accessibility testing

• No accessibility behavior change expected. This change only updates runtime font refresh behavior for controls using the default/inherited font.

Test environment(s)

• Windows 11
• .NET SDK: 11.0.100-preview.3.26170.106

Microsoft Reviewers: Open in CodeFlow