Revert "Remove ExperimentalCoroutinesApi and FlowPreview opt-in"

Author: SimonMarquis

build-logic/convention/src/main/kotlin/com/google/samples/apps/nowinandroid/KotlinAndroid.kt

@@ -88,6 +88,9 @@ private fun Project.configureKotlin() {
             allWarningsAsErrors = warningsAsErrors.toBoolean()
             freeCompilerArgs = freeCompilerArgs + listOf(
                 "-opt-in=kotlin.RequiresOptIn",
+                // Enable experimental coroutines APIs, including Flow
+                "-opt-in=kotlinx.coroutines.ExperimentalCoroutinesApi",
+                "-opt-in=kotlinx.coroutines.FlowPreview",
             )
         }
     }