Diff each status against the previous version, comparing the different
HTML as XML to produce a structured diff.

Mark new content with `<ins>`, deleted content with `<del>`.

Convert these to styled spans in `ViewEditsAdapter`.

Fixes issue with diffs splitting on accented characters

Don't use HTML spans and try and format them, create real Android spans.

Do this with a custom tag handler that can add custom spans that set the
text paint appropriately.

Make the background slightlysofter by drawing it as a roundrect.

Make the spans easier to understand by padding the start/end of each one with
the width of a " " character. This is visual only, the underlying text is not
changed.

# Conflicts:
#	app/src/main/java/com/keylesspalace/tusky/components/viewthread/edits/ViewEditsViewModel.kt

A ReplacementSpan can't cover multiple lines, so if the modified text was
more than a line it ran off the end of the screen.

https://medium.com/androiddevelopers/drawing-a-rounded-corner-background-on-text-5a610a95af5
suggests a fix which involves a custom textview.

- Show the most recent version in larger text, both to make the most recent
  version clearer, and for consistency with the thread view (where the version
  the user clicked in will also have been shown in larger text)
- Scroll the most recent version in to view
- Show a pinned header with the author's avatar, display name, and username
  in one place, instead of duplicating this information in each version of
  the status.

# Conflicts:
#	app/src/main/java/com/keylesspalace/tusky/components/viewthread/edits/ViewEditsAdapter.kt
#	app/src/main/java/com/keylesspalace/tusky/components/viewthread/edits/ViewEditsViewModel.kt

…d/edits/ViewEditsViewModel.kt

…dits

# Conflicts:
#	app/src/main/res/values/strings.xml

- Resolve lint errors

…n/Tusky into 3306-diff-status-edits

# Conflicts:
#	app/src/main/java/com/keylesspalace/tusky/components/viewthread/edits/ViewEditsViewModel.kt
#	app/src/main/res/values/strings.xml