Make Jetpack Compose extension multiplatform

[jakobkmar]

The Jetpack Compose extension seems to be Android only at the moment, but Compose Color is actually multiplatform and defined in the commonMain part of compose.ui.graphics.

Therefore I don't see the need for this extension to be Android only here. Making it multiplatform would allow the extension to be used for compose-jb as well.

Thanks in advance!

[ajalt]

That's a good idea. I'd welcome a PR.

[ajalt]

Thanks for the suggestion, I implemented this in 4b1f896