[macOS] Adding theme tokens (#2168)

* Adding tokens for macOS

* Revert change for platformColorValue

* Fixing build

* Addressing comments

* Moving ColorTokens out of common

* Sync PRs

* Use @available

* Addressing comments

* Remove extra line

* Addressing comments

Author: DanielMorM

Demos/FluentUIDemo_macOS/FluentUISwiftUITestApp/ContentView.swift

@@ -15,6 +15,9 @@ struct ContentView: View {
 						Text(testViewController.title)
 					}
 				}
+				NavigationLink(destination: TestAliasColorTokensViewController()) {
+					Text("Alias Color Tokens")
+				}
 			}
 			.listStyle(SidebarListStyle())
 		}