Migrate JavaScript source files to TypeScript

[TimPurdum]

To better support writing and maintaining the growing source code, we want to move the JavaScript files to TypeScript. Compile and Build TypeScript Code describes how to add a nuget package that will automatically compile .ts files along with .NET compilation.

1. Add the nuget package referenced above.
2. Convert all existing .js files to a .ts file.
3. Organize .ts files in a Scripts folder.
4. Import type definitions from esri: Using TypeScript with the ArcGIS API for JavaScript.
5. Update code to include function and object types.