Ensure Dispatchers.Main != Dispatchers.Main.immediate on Android

Fixes #3545

Author: dkhalanskyjb

ui/kotlinx-coroutines-android/src/HandlerDispatcher.kt

@@ -169,8 +169,9 @@ internal class HandlerContext private constructor(
         if (invokeImmediately) "$str.immediate" else str
     }
 
-    override fun equals(other: Any?): Boolean = other is HandlerContext && other.handler === handler
-    override fun hashCode(): Int = System.identityHashCode(handler)
+    override fun equals(other: Any?): Boolean =
+        other is HandlerContext && other.handler === handler && other.invokeImmediately == invokeImmediately
+    override fun hashCode(): Int = System.identityHashCode(handler) xor invokeImmediately.hashCode()
 }
 
 @Volatile

ui/kotlinx-coroutines-android/test/HandlerDispatcherTest.kt

@@ -132,4 +132,11 @@ class HandlerDispatcherTest : TestBase() {
         mainLooper.scheduler.advanceBy(51, TimeUnit.MILLISECONDS)
         finish(5)
     }
+
+    @Test
+    fun testHandlerDispatcherNotEqualToImmediate() {
+        val main = AndroidDispatcherFactory().createDispatcher(listOf())
+        val immediate = main.immediate
+        assertNotEquals(main, immediate)
+    }
 }