fix(grid): add background-clip to filtering cell style - master

[IMinchev64]

Closes #16639

Additional information (check all that apply):

• Bug fix
• New functionality
• Documentation
• Demos
• CI/CD

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them

[desig9stein]

@IMinchev64 The issue persists for pinned columns; the selection state isn't visible on the header cell. I recommend using an ::after pseudo-element to handle the selection styling. Since we already refactored this in the scoped styles branch, you can refer to this PR for our implementation logic.

Let me know if you have any questions