Fix ProgressBar dark mode rendering inconsistency across style variants

[LeafShi1]

Fixes #14546

Root Cause

The native themed ProgressBar rendering on newer Windows builds applies style-dependent visual effects in dark mode. As a result, Blocks, Continuous, and Marquee do not share a single consistent rendering path. When the control depends on native theming, the background and foreground colors can diverge across styles.

Proposed changes

• Disable native ProgressBar theming in dark mode and drive ProgressBar colors through explicit color messages.
• Reapply theming and colors after handle recreation, style changes, color changes, and user-preference updates.
• Use SystemColors.ControlText as the dark-mode background color to satisfy contrast requirements.
• Preserve system-controlled ProgressBar colors in the classic/native rendering path.
• Apply explicit ProgressBar colors only in the dark-mode workaround path used to ensure consistent rendering across style variants.

Customer Impact

• Fixes inconsistent ProgressBar appearance in dark mode and improves readability and contrast between the progress fill and background.

Regression?

• No

Risk

• Minimal

Screenshots

Before

Blocks, Continuous, and Marquee render with different visual results.

Recording.2026-05-20.095837.mp4

After

Three ProgressBar styles (Blocks, Continuous, Marquee) render with consistent colors in dark mode and color changes and style switching work correctly

AfterChanges.mp4

Test methodology

• Manually

Test environment(s)

• .net 11.0.0-preview.5.26268.112

Microsoft Reviewers: Open in CodeFlow

[SimonZhao888]

Looks good to me!

[Copilot]

Pull request overview

This PR updates WinForms ProgressBar dark-mode behavior to avoid Windows 11 (25H2+) style-dependent themed rendering differences by disabling native theming in the affected cases and explicitly driving bar/background colors via PBM color messages, reapplying this on handle recreation and relevant system/user changes.

Changes:

• Centralizes dark-mode/custom-color handling in ApplyTheming() and calls it from handle creation, style changes, color changes, and user preference updates.
• Introduces “effective” back/fore color helpers to ensure consistent default colors (including a dark-mode default background).
• Removes the prior OnCreateControl-time dark-mode workaround in favor of handle-based reapplication.

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