CodeViewer: Implement HeaderContent

[mckaragoz]

Fix#633

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.38%. Comparing base (12572c0) to head (8363894).

Files with missing lines	Patch %	Lines
...zor.Extensions.Code/Components/MudCodeViewer.razor	50.00%	1 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@ Coverage Diff @@## dev #640 +/- ##
==========================================
- Coverage 65.41% 65.38% -0.03% 
==========================================
Files 111 111 Lines 8379 8381 +2 Branches 1479 1480 +1 ==========================================
- Hits 5481 5480 -1 - Misses 2392 2394 +2 - Partials 506 507 +1 

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.