Upgrade tagetSdkVersion to Android 31

[danilo04]

Fixes ##1570.

Fix

Upgrade to targetSdkVersion = 31 and compileSdkVersion = 31. Following the recommendations for the upgrade, we were affected by the following:

• Intent filters: If your app contains activities, services, or broadcast receivers that use intent filters, you must explicitly declare the android:exported attribute for these components.
• Pending intent mutability: You must specify the mutability of each PendingIntent object that your app creates.

We apply the following changes to support the new targetSdkVersion:

• Upgrade androidx.work:work-runtime to 2.7.1. The previous version was crashing the app because immutability of pending intents.
• Ad immutable flag to pending intents. In one case (widgets) we need mutable pending intents.
• Added exported:true to components that use intent filters.

Test

Smoke test the whole app.

• Test notes, adding, editing, opening links, etc.
• Add collaborators
• Add tags
• Setup lock screen
• Import/Export
• Widgets

Review

Only one developer is required to review these changes, but anyone can perform the review.

Release

RELEASE-NOTES.txt was updated in a7465aeee3a84990e006b6038b633b28acf1728e with:

Upgrade to targetSdkVersion 31 (Android 31)

[wpmobilebot]

You can test the changes on this Pull Request by downloading an installable build (simplenote-android-installable-build-pr1571-a7465ae-01848c85-1dc2-48db-a9be-5744215fac70.apk), or scanning this QR code:

[matthewejohnson711]

sounds good