Add snippets for Android Wear's Always On doc

[ithinkihaveacat]

Will be used here: https://developer.android.com/training/wearables/always-on

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• wear/src/main/java/com/example/wear/snippets/alwayson/AlwaysOnActivity.kt:101, tag android_wear_ongoing_activity_elapsedtime
• wear/src/main/java/com/example/wear/snippets/alwayson/AlwaysOnActivity.kt:148, tag android_wear_ongoing_activity_ambientaware
• wear/src/main/java/com/example/wear/snippets/alwayson/AlwaysOnService.kt:96, tag android_wear_ongoing_activity_create_notification

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[kul3r4]

Added 2 suggestions if you are able to incorporate those!