[eslint] Prefer TypeScript `interface` over type aliases.

We have a mix of `type` and `interface` usage throughout our codebase,
that is sometimes difficult to follow and reason about. We should follow
the suggestion from the TypeScript PM and use `interface` consistently
where possible. This leads to better type display in errors and makes
our codebase easier to read (b/c consistency).

This CL adds the `etc/prefer-interface` ESLint rule to accomplish this.

Fixed: 387237537
Change-Id: Idd6775094ba94b8397f626191788437f6b156dc6
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6135001
Commit-Queue: Nikolay Vitkov <nvitkov@chromium.org>
Reviewed-by: Nikolay Vitkov <nvitkov@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>