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 modifies the `structure` syntax so that parents can be named,
like in
```lean
structure S extends toParent : P
```
**Breaking change:** The syntax is also modified so that the resultant
type comes *before* the `extends` clause, for example `structure S :
Prop extends P`. This is necessary to prevent a parsing ambiguity, but
also this is the natural place for the resultant type. Implements RFC
#7099.
Will need followup PRs for cleanup after a stage0 update.
