* 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);
```
* Optimize sourcemap application more
* Remove test-only memory hog sourceMapDecodedMappings field
* Update for style, remove unused function that triggers warnings in node 10
* Avoid all raw buffer constructor calls
* Small TDZ fix
