[Handlers] Map CornerRadius property in ButtonHandlers

[jsuarezruiz]

Description of Change

Map CornerRadius property in ButtonHandlers.

Platforms Affected

• iOS
• Android

PR Checklist

• Targets the correct branch
• Include handlers tests
• Tests are passing (or failures are unrelated)

[hartez]

I think we should hold off on this one until we have a better handle on what we're doing with shapes. If we can do a generic clip shape at the MAUI level, then we won't need to add a specific CornerRadius property; we can keep that at the Controls level and implement it using the clip shape.

[GalaxiaGuy]

If this does ahead (I don't know what the plan is with shapes), should it be based on this:

dotnet/maui#10

[hartez]

Going to close this for now; we're close to having the underlying parts in MAUI that we can look at doing clipping shapes again for universal rounded/beveled/whatever edges on things.

If we decide not to go that direction, we can re-open and port this PR.