feat(grid): style inputs in the context of cell

[didimmova]

Closes #16360

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

[Copilot]

Pull Request Overview

This PR adds styling overrides for input components within grid cells to ensure proper visual integration. The changes apply to various Ignite UI input components (input-group, combo, select, date/time pickers) to make them display correctly within the grid cell context.

Key changes:

• Extends cell input overrides placeholder
• Sets height to 'auto' for multiple input component types within cells
• Applies transparent background to igx-input-group components

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