An unannotated `const xs = []` (or `let`) inside a function, which
TypeScript types by the elements written before each read, takes the array
type its settled reads have: records pushed in a loop give a record array,
numbers a number[], strings a string[]. Reads inside closures, which the
checker leaves unsettled, do not count. When settled reads disagree or the
binding is reassigned, the binding is a dynamic array, as the same binding
already is at module scope. Before, such a binding was always number[] and
pushes of other values were refused.
Fixes#1623
Co-authored-by: ejc3 <1694850+ejc3@users.noreply.github.com>
