Documentation(856747): Fixed Filtering sample formatting and added Filtering event documentation in the Blazor ListBox UG

[kathiravan4982]

Description

Documentation(856747): Fixed the following issues in the Blazor ListBox Filtering UG documentation:

• Fixed the indentation issue in the FilterType sample code block by properly aligning the LocalData declaration and new Games() list items.
• Updated the LocalData declaration with an explicit access modifier to follow the documentation sample coding pattern.
• Added a Custom filtering section with a Filtering event example to demonstrate customized filter query handling in the Blazor ListBox component.
• Added proper API reference links and descriptions for the Filtering event, FilteringEventArgs, PreventDefaultAction, and FilterAsync method.

The FilterType API reference link was reviewed and retained without changes. The FilterType property is not listed in the ListBox-specific API page, so the existing link is required to navigate users to the correct API reference page where the property definition, supported filter type values, and filtering behavior details are available.

Code Studio usage(Mandatory)

• Code Studio used in this PR/MR?

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  • No

• If Yes: Primary use (choose one)

  • Generate new content
  • Refactor/improve existing content
  • Review assistance (explanations/summaries)
  • Other:

• Outcome

  • Saved time
  • Neutral
  • Cost time

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Type of Change

• New documentation page
• Update to existing documentation
• Bug fix (broken links, typos, formatting issues)
• Structural change (folders, navigation, index)
• Content improvement (clarity, examples, screenshots)
• Other (please describe):

Reviewer Checklist (Mandatory)

• Reviewed the provided Code Studio usages related information
• Content changes follow UG/Documentation guidelines
• All provided information reviewed and verified
• Links and previews checked

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: 856747-ListBoxUG

[SyncfusionBuild]

CI Status: SUCCESS ✅
Source Compilation: SUCCESS ✅
Build Location: 856747-ListBoxUG
Technical Error(s): 0
Spelling Error(s): 0
Image Alt Text Error(s): 0
Image Size Error(s): 0
Image Name Error(s): 0
Front matter Error(s): 0
File Path Error(s): 0
CodeSnippet File Path Missing Error(s): 0
Toc Anchor Tags Validation Error(s): 0
MD Tag Validation Error(s): 0