Button dropshadow style introduction

[tristanjasper]

Feature request

Dropshadow style to be added to Button. (As required in new results collection page table and action bar)

Currently I am approaching with a style override (https://github.com/acl-services/acl-exception/pull/7938)

But we need a better approach.

Prerequisites

This is just a checklist, please delete this section after Please answer the following questions for yourself before submitting a feature request.

• [ ] I checked to make sure that this feature has not already been suggested
• [ ] Please label as, low / medium / high priority

Please fill in as much detail as possible

Is your feature request related to a problem?

A clear and concise description of what the problem is

Describe the solution you'd like

A clear and concise description of what you want to happen.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context or screenshots about the feature request here.

[tristanjasper]

@sunminsarahlee Can you elaborate on your needs for the ActionBar with regards to this feature? So I can cover all requirements when adding.

[sunminsarahlee]

We just need to make sure our flat button in paprika has drop shadow so all our flat button in platform will have drop shadow. And those changes also should be applied for ActionBar new design.