This reverts commit 231d97ea.

Migrating to AndroidX Fragments seems to have some unforseen side effects
and no clear benefits

on device contacts (contacts not synced) have an unstable system uri.
For quicksy.im contacts we can identify the contact based on the phone number
instead.

fixes #4174

fixes #4165

fixes #4167

the transcoder library we used hasn’t been updated in years

this commit switches to a maintained fork https://natario1.github.io/Transcoder/

This reverts commit 8d45cc58.

"uuid" is a primary key in "messages" but not in "messages_index",
the implication of that is very slow matching by UUID.

What can be done instead is matching messages_index.rowid to messages.rowid,
that is, an always-present clustered index.

This not only improves performance of full-text search but also of just
updating messages in any shape or form.

It now uses the data from the messages table instead of having a copy of each
message.

The message UUIDs are no longer part of the index.

If we don’t executePendingTransactions we might still access the overview fragment
while a replacement operation is in the works. This will lead to two
conversationfragments opening.