…ork with mocha 8+

Component commits:
97cb818 No contextual types from circular mapped type properties

1dcf4ab Add regression test

Co-authored-by: Anders Hejlsberg <andersh@microsoft.com>
Co-authored-by: Wesley Wigham <wwigham@gmail.com>

….prototype.flat (#38904) (#39079)

* Add declaration emit error and checking for circularly referential unions produced by recursive conditionals

* Allow indexed accesses to produce alias symbols on types

* Add test that still triggers the declaration emit error

* Fix spelling

Neither `x[0]` nor `x[(0)]` should be dynamic names. Previously, the
latter was because `isDynamicName` didn't skip parentheses.

Since the binder treats dynamic names in property assignments as
assignment declarations, this incorrectly tried to create a binding for
expressions like `x[(0)] = 1`.

This caused an assert because `x[(0)]` would not take the dynamic name
code path during binding (`hasDynamicName` returned false), but the
normal code path for static names.