Add support for Contact LOOKUP_KEY

[vestrel00]

As the official documentation states, ContactsContract.ContactsColumns#LOOKUP_KEY is...

An opaque value that contains hints on how to find the contact if its row id changed as a result of a sync or aggregation.

This will be useful for consumers that want to save a reference to a Contact in order to load it later. Currently, the only way for consumers to do this is via the Contact.id, which could change "as a result of a sync or aggregation".

Problem

Here is a common scenario that could occur,

1. Consumer app shows details of Contact with ID of 7.
2. Consumer app is backgrounded.
3. Another Contacts app is opened.
4. The Contact with ID of 7 is forcefully linked to another Contact in the other Contacts app.
5. The Contact with ID of 7 is now aggregated to a Contact with ID of 11.
6. Consumer app is resumed and tries to recreate the activity, reloading the Contact with ID of 7.
7. Consumer app shows that it is unable to find that Contact.

Solution

Implement Contact.lookupKey so that consumers can save a reference to a Contact that can be held long term.

• Document that lookup key is not a required field like the IDs. This allows memory optimizations for certain queries as lookup keys are strings that can be lengthy.
• Update sample app to use lookup key instead of ID
• Document Contact lookup key behavior for associating local contacts (not associated with an Account) with an Account and vice versa.
• Document Contact lookup key behavior when linking/unlinking.
• Document Contact lookup key vs id.
• Document RawContacts DOES NOT have a lookup key.
• Mention getting contacts by lookup key vs ID in howto page for Query.
• Verify implementation on minSdkVersion (API 19)
• Verify implementation on targetSdkVersion (API 31)

Notes

As mentioned in #139, it seems like the LOOKUP_KEY is the same across devices as long as data has been synced (up-to-date) with the servers!

This is probably also required to implement #70 .

[vestrel00]

I'm doing a lot of research and documentation here! It is definitely tougher than just coding 😭 But I WILL PERSEVERE FOR THE COMMUNITY ❤️ 🔥

[vestrel00]

This is released in https://github.com/vestrel00/contacts-android/releases/tag/0.2.0