[Feature] Add taskbar widget overlap prevention feature

[koiseka]

Summary

This PR introduces an optional overlap-prevention feature for the Taskbar Widget in left alignment mode.
When enabled, FluentFlyout detects available space before the Start button and shrinks widget width as needed to avoid overlap in constrained taskbar layouts.

Motivation

On small taskbars or when many apps are pinned or running, the left-aligned taskbar widget can overlap with Start-area UI.
This change improves layout reliability and user control by adding a dedicated setting to prevent overlap only when needed.

Partially addresses #447 by reducing taskbar widget overlap in constrained layouts via optional Start-boundary-aware width clamping.

Type of Change

• Feature
• Bug fix
• Refactor (no functional changes)
• Style (formatting, naming)
• Other

What Changed

• Added a new user setting: TaskbarWidgetPreventStartOverlap (default: off).
• Added a new toggle in Taskbar Widget settings UI for overlap prevention (left alignment only).
• Implemented Start-button-aware overlap prevention in taskbar widget positioning.
• Resolves Start button bounds using UI Automation.
• Validates Start bounds before applying clamping to avoid false-positive matches.
• Shrinks widget width only when overlap would occur.
• Preserves existing placement behavior when overlap prevention is disabled or Start bounds are unavailable.
• Extended taskbar element lookup helper to support property-based lookups for safer Start detection.
• Added English localization strings for the new setting.

Additional Information

All screenshots were captured on the same monitor/taskbar scale for direct comparison.

Before (Windows Widgets disabled)

After enabling overlap prevention (Windows Widgets disabled)

Before (Windows Widgets enabled)

After enabling overlap prevention (Windows Widgets enabled)

Checklist

• Code changes are manually tested and working.
• Formatting and naming are consistent with the project.
• Self-review of changes is done.
• AI tools were used (if yes, I reviewed and fully understand the changes myself).

[Trollcraft1002]

Hello, I tested the PR build locally.

The overlap prevention seems to work for the main music/taskbar widget, but it does not appear to work for the taskbar visualizer / volume visualizer area.

In the first screenshot, the media widget is positioned correctly and does not overlap the pinned taskbar icons:

In the second screenshot, however, the visualizer still overlaps the pinned taskbar icons and blocks interaction with them:

For now the solution is to use Bottom Left option on the "Visualizer Position Relative to Taskbar Widget"