Replace app engine js compilation with ts-node

[codersasha]

Replace app engine js compilation step with running ts-node on the app engine server.

As ts-node gains popularity, the benefits of debugging and instrumenting typescript code in real-time justify skipping compilation to JS altogether.

Not sure if this has already been considered. Also note that repo-tools test may not support testing typescript code directly, although many popular typescript testing libraries (e.g. jest) do support this.

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[codersasha]

@googlebot I signed it!

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[fhinkel]

@sashamor Thanks for the pull request. In our docs, we want to explicitely show how to compile TypeScript sources instead of using ts-node. Thank for understanding.