[Feature]: New size for buttons to match Outlook densities needs

Package

Other...

Describe the feature that you would like added

Outlook has some different needs because of the different densities. It needs a size that sits between Small and Medium. Right now, engineers are having to hard-code a custom size, which introduces extra maintenance and risks drifting from Fluent standards

Reference links:
Specs and comparisons here: https://www.figma.com/design/kH8NfE22oaceEprpQtKyVz/Buttons-for-densities?node-id=1499-2774&t=gwGLSodQvh5iWrvo-4

Additional context

PM spoke with the Fluent development team. They confirmed that this request is not a breaking change for engineering. They mentioned it could be implemented as a "variant," which should be straightforward. If this is very specific to Outlook, it should be added to the Fluent-contrib repository. Engineering estimated it could be completed in one-two days.

The Fluent Prague Team currently has no capacity, so Outlook should contribute this change. The Prague team will support with PR resolution to help expedite the process.

Have you discussed this feature with our team

@gouttierre @marcosmoura

Validations

• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.

Priority

Medium

Start in the Fluent-contrib repository by locating the button package and its existing Small and Medium size or variant definitions. Review the linked Figma specifications and compare the current button tests or examples. Done means the intermediate Outlook density size is available without hard-coded custom sizing and is covered by the relevant tests.