MAUI - SfDataGrid - Addressed correction for MultiColumnComboBox column

[ArunaSF4759]

Description

• Addressed the changes for MultiColumnComboBox column by adding border to the filtering image.
• Added API link for FreezePanesLineStrokeThickness

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: MAUI-MultiColumnComboBox-Corrections

[SyncfusionBuild]

CI Status: SUCCESS ✅
Source Compilation: SUCCESS ✅
Build Location: MAUI-MultiColumnComboBox-Corrections
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