Make Compile On Save on by default for loose files

[danquirk]

Currently you need to go into Tools -> Options -> Text Editor -> TypeScript -> Project -> General in order to turn on Compile on Save for non-project contexts. It's not clear why we wouldn't just want this on by default there when we have it on by default for projects. We would need to pick a codegen target which we could do through inspection (if you are an external module use commonjs, else use amd). In any case, some number of people might have to change the codegen target from the default but that's fewer people than are currently having to go in and do the exact same set of clicks to turn it on in the first place.

[RyanCavanaugh]

👍

[mhegazy]

with tsconfig.json being the main way of configuring projects, configuration for loose files seem to be less important. also starting with TS 1.8, you can have multiple tsconfig.json files for your projects, and "compileOnSave" property in tsconfig.json controls compile on save separately for each tsconfig.json file.

see : #5287
and https://github.com/Microsoft/TypeScript/wiki/tsconfig.json#compileonsave