refactor(input-group): add styling support for more input types

[simeonoff]

Closes #17156

Description

This PR adds minimal styling support for input types date, time, datetime-local, month, and week in the context of the igx-input-group component.

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog
• Skills/Agents

Component(s) / Area(s) Affected:

The only affected component is the Input Group.

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

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
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

[Copilot]

Pull request overview

Adds styling support in igx-input-group for native date/time-like input types to prevent label/placeholder overlap (Issue #17156), and updates the showcase to demonstrate the newly supported types.

Changes:

• Updated the Input Group showcase sample to include date, time, datetime-local, month, and week native input types (and adjusted defaults).
• Extended Material/Bootstrap input-group styling selectors to account for date/time-like inputs (label/notch behavior, disabled text coloring).
• Introduced color-scheme propagation based on theme variant to better align native control rendering with theme mode.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/app/input-group-showcase/input-group-showcase.sample.ts	Expands the demo’s selectable native input types and adjusts default selections.
projects/igniteui-angular/core/src/core/styles/components/input/_input-group-theme.scss	Adds styling rules for date/time-like native inputs to avoid label overlap and improve visual consistency.

[adrianptrv]

There is a difference in the text colors for the idle state across the input types
In Angular, the text uses --filled-text-color for both the idle and filled states, while in WC it uses --idle-text-color for the idle state and --filled-text-color for the filled state.