Added two extension functions for StateIn

There are two extension functions in this file, one is for ViewModels, and another one for using within a CoroutineScope.

core/ui/src/main/java/com/google/samples/apps/nowinandroid/core/ui/Extenstions.kt

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.samples.apps.nowinandroid.core.ui
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.stateIn
+
+/**
+ * This is a helper extension function to make it easier to use [Flow.stateIn] within a ViewModel.
+ * @Returns a [StateFlow] that shares the latest value emitted by the original [Flow] and starts
+ * with the [initialValue].
+ */
+fun <T> Flow<T>.stateInViewModelScope(
+    viewModelScope: CoroutineScope,
+    started: SharingStarted = SharingStarted.WhileSubscribed(5_000),
+    initialValue: T
+): StateFlow<T> = stateIn(viewModelScope, started, initialValue)
+
+/**
+ * This is a helper extension function to make it easier to use [Flow.stateIn] within a [CoroutineScope].
+ * @Returns a [StateFlow] that shares the latest value emitted by the original [Flow] and starts
+ * with the [initialValue].
+ */
+fun <T> Flow<T>.stateInCoroutineScope(
+    viewModelScope: CoroutineScope,
+    started: SharingStarted = SharingStarted.WhileSubscribed(5_000),
+    initialValue: T
+): StateFlow<T> = stateIn(viewModelScope, started, initialValue)