This PR migrates most remaining tests to the new test suite. It also
completes the migration of directories like `tests/lean/run`, meaning
that PRs trying to add tests to those old directories will now fail.
This PR adds auto-completion for identifiers after `end`. It also fixes
a bug where completion in the whitespace after `set_option` would not
yield the full option list.
Closes#3885.
### Breaking changes
The `«end»` syntax is adjusted to take an `identWithPartialTrailingDot`
instead of an `ident`.