Implement OS color scheme auto-detection for new users

[mrleemurray]

Introduce a feature that automatically detects the OS color scheme for new users, ensuring a seamless experience without requiring explicit configuration. Add tests to verify the detection logic for high contrast themes.

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@bpasero

Matched files:

• src/vs/platform/windows/electron-main/windowsMainService.ts

[Copilot]

Pull request overview

Adds first-run OS color scheme auto-detection so fresh installs pick light/dark (and high-contrast) automatically, and wires this through both renderer theme selection and the Electron main-process nativeTheme configuration.

Changes:

• Extend ThemeConfiguration with “new user” logic to treat window.autoDetectColorScheme as enabled when unset on first run.
• Persist window.autoDetectColorScheme=true for new installs (migration) so the behavior becomes stable across restarts.
• Update Electron main-process theme plumbing to default autoDetectColorScheme from a new IThemeMainService.isAutoDetectColorScheme() helper.
• Add unit tests covering new-user auto-detect behavior, including high-contrast priority cases.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/vs/workbench/services/themes/test/common/workbenchThemeService.test.ts	Adds unit tests for new-user scheme detection and HC priority behavior.
src/vs/workbench/services/themes/common/themeConfiguration.ts	Introduces isNewUser and new auto-detect decision logic.
src/vs/workbench/services/themes/browser/workbenchThemeService.ts	Passes “new user” signal and migrates/persists auto-detect setting for new installs.
src/vs/platform/windows/electron-main/windowsMainService.ts	Defaults window config’s autoDetectColorScheme using main theme service helper.
src/vs/platform/theme/electron-main/themeMainServiceImpl.ts	Implements isAutoDetectColorScheme() and uses it to drive nativeTheme decisions.
src/vs/platform/theme/electron-main/themeMainService.ts	Extends main theme service interface with isAutoDetectColorScheme().