Closes #16087 [Part of Alignment with WC date range picker]

• adds built-in igx-picker-clear for single input
• abstracts the click event subscription in the PickerBase, so that all picker elements could respond to a clear action by a projected igx-picker-clear
• two inputs remain unchanged by default - their template is the input group's, so no built-in elements will be enforced. The icons can be projected by users, if required. Logged a task to modify the samples to include toggle & clear icons, to keep them aligned to the WC DRP.
• adding the built-in clear icon also led to the following change, which is intentional and corresponds to the WC DRP - before for single input, the click over the entire input opened the calendar even in dropdown mode (in dialog it should be like this). Now the picker is opened when clicking the toggle icon and not the input in dropdown mode for singe input.
• For two inputs in dialog mode, the picker should be opened by clicking the toggle icon or the inputs (ref).

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