* Add full implemention of Map and Set to shims
* Update default Map interface
* Remove WeakMap/WeakSet
* Add tests for set shim
* Update most usages of Map<K, true> to Set
* PR Feedback
* Fix lint issues
* Change key in fsWatchCallback
* Simpler shim, more tests
* Fix typo in collection shim
* Rename JS concepts
1. Assignment declaration -- an assignment that is treated like a
declaration. Previously called [JS] special (assignment|declaration),
among other things.
2. Expando -- a value that can be used as a target in assignment
declarations. Currently, a class, function or empty object literal.
Functions are allowed in Typescript, too. Previously called a JS
container, JS initializer or expando object.
3. JavaScript -> Javascript. This is annoying to type, and looks like
'Java Script' in a camelCase world.
Everything is a pure rename as far as I know. The only test change is
the API baselines, which reflect the rename from SymbolFlags.JSContainer
to SymbolFlags.Assignment.
* Remove TODO
* Rename Javascript->JS
Note that this introduces a variable name collision in a couple of
places, which I resolved like this:
```ts
const isInJavascript = isInJSFile(node);
```
