Implement Display Density for the IgxDropDownComponent

[tachojelev]

Is your feature request related to a problem? Please describe.

In order to support the display density for the Excel Style Filtering across all its sub-components and sub-dialogs, we need IgxDropDown to implement the display density functionality.

Describe the solution you'd like

Either the dropdown component or its dropdown-item components (or both) should probably extend the DisplayDensityBase class.

Describe alternatives you've considered

N/A

Additional context

[ViktorSlavov]

Duplicate of #2960
Once we have a spec for display density in drop-down items, we will implement it for combo, drop-down and select items