Scroll services: Clean up, make implementations internal, add xmodoc

[ScarletKuro]

Description

Improves overall code quality
The implementation should always be internal.
Removed ScrollOptions and ScrollManagerException as it wasn't used anywhere.

Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

Attention: Patch coverage is 79.16667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 91.10%. Comparing base (ed81ebe) to head (8e6475f).

Files with missing lines	Patch %	Lines
src/MudBlazor/Services/Scroll/ScrollSpy.cs	0.00%	3 Missing ⚠️
src/MudBlazor/Services/Scroll/ScrollListener.cs	80.00%	0 Missing and 1 partial ⚠️
src/MudBlazor/Services/Scroll/ScrollManager.cs	88.88%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #10048   +/-   ##
=======================================
  Coverage   91.10%   91.10%           
=======================================
  Files         409      410    +1     
  Lines       12486    12488    +2     
  Branches     2423     2424    +1     
=======================================
+ Hits        11375    11377    +2     
  Misses        566      566           
  Partials      545      545           

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[ScarletKuro]

Added to the v8 migration guide at #9953