Support more file extensions (.gts,.svelte,.vue,etc)

Hello,

I'm developing in Ember. Ember (as many other frameworks) do use a custom js-dialect and I wrote a typedoc plugin to parse ember files. I also did wrote an ember-docgen package that uses typedoc under the hood. Now I'm using both to make ember work with storybook.

Problem

In order to support custom extensions, one must "hack" into typescript to allow for other extensions and append .ts to the filename, so it works with typedoc.

Here are my projects:

• https://github.com/ember-integrations/ember-storybook/tree/184eb214d42e4305a34f87db9381761e82d04131/packages/typedoc-plugin-ember
• https://github.com/ember-integrations/ember-storybook/tree/184eb214d42e4305a34f87db9381761e82d04131/packages/ember-docgen

Running an own typescript instance is quite error prone.

Suggested Solution

I'd prefer an option to typedoc to allow for more extensions, too. As plugins can provide parser to it, in the same breath they should be able to add the supported extension, too. So end users only need to add the plugin and are covered.

Start by tracing how TypeDoc discovers and parses TypeScript files, then inspect the plugin parser extension point described in the issue. Determine how a plugin could register extensions such as .gts, .svelte, and .vue without running a separate TypeScript instance. Done means a plugin can declare its supported extensions and TypeDoc processes those files through its parser.