Replace editor icon with branding admin menu icon

[ilicfilip]

We had PP icon hard coded on Editor screen (it is used to toggle PP sidebar). This PR does following:

• Replace hardcoded SVG icon in block editor with branding-aware icon from the branding system
• Add $raw parameter to get_admin_menu_icon() to return either base64 data URI or raw SVG markup
• Render icon as inline SVG for CSS styling support (white icon when sidebar is active)

[github-actions]

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[github-actions]

✅ Code Coverage Report

Metric	Value
Total Coverage	31.61% 📉
Base Coverage	31.61%
Difference	📈 0.00%

⚠️ Coverage below recommended 40% threshold

🎉 Great job maintaining/improving code coverage!

📊 File-level Coverage Changes (2 files)

📈 Coverage Improved

Class	Before	After	Change
Progress_Planner\UI\Branding	33.33%	33.64%	+0.31%

📉 Coverage Decreased

Class	Before	After	Change
Progress_Planner\Admin\Editor	4.76%	4.55%	-0.21%

ℹ️ About this report

• All tests run in a single job with Xdebug coverage
• Security tests excluded from coverage to prevent output issues
• Coverage calculated from line coverage percentages