TypeScript support

[epixa]

Before we can start using TypeScript, we need proper support for TypeScript in our build system. The compilation process should be handled through the same process that handles our ECMAScript compilation, so people can develop using both TypeScript and ECMAScript simultaneously without juggling build tasks.

We should not ship TypeScript with builds of Kibana, so we can't simply add this to the existing optimizer. Effectively, this means we must first remove the optimizer.

edit: We are going to add support for TypeScript to the optimizer during development and will transpile code from TS to JS while building the distributable (and plugin distributables), just like we transpile all JS with babel to lighten the load of babel-register and the optimizer in production.

Blocked by #7322

[epixa]

@elastic/kibana-operations