[New Platform Migration Phase I]: convert timelion. Migrate server part

[alexwizp]

Partually fix: #41667

Summary

First step of migrating to the new Platform. In this PR was migrated only server part of timelion plugin

What was done in this PR:

• Have a new platform-style server plugin definition in typescript, with a setup method returning the public contract (see data plugin as an example). This needs to be exported from the top-level /server and/or /public directory, e.g. export foo = new Plugin.setup()
• Removed init.js file. Logic was refactored and was moved to plugin.ts
• Use server.expose instead of unsafe:

 server.plugins.timelion = {
    functions: functions,
    addFunction: addFunction,
    getFunction: getFunction
  };

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-app-arch

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request

[lukeelmers]

Code overall LGTM, tested Chrome OSX and not finding any issues.

[lukeelmers]

I didn't realize we had an old .editorconfig in here!