More precise TS types in ecmascript.ts

This commit makes ecmascript.ts changes for TS:
* Support `strictNullChecks: true`. This means that any type
  that could possbly be undefined or null needs to be declared as
  such. This leads to a lot of types needing to be redefied to add
  or to exclude `undefined`.
* Support `strictPropertyInitialization: true`. This means that all
   variables must be explicitly declared before they're used.
* Remove use of `any` and replace with more precise types.

Unlike calendar.ts, there were no bulk renames in this file. Just
lots of one-off changes.

Author: justingrant