[lexical-playground] [minor] Feature: turn single-file plugins `plugins/*Plugin/index.tsx` into `plugins/*Plugin.tsx`

[vadimkantorov]

Similar to https://github.com/facebook/lexical/blob/main/packages/lexical-playground/src/plugins/TablePlugin.tsx

The import statements like import LinkPlugin from './plugins/LinkPlugin' do work with both single-file and directory style, but the non-index.tsx-named plugin files are a tiny bit more convenient to manage in custom user codebases which copy/sync these plugins code from Playground.

Out of 50 plugin dirs currently, only 13 plugins are multi-file, the remaining 37 are single-file index.tsx ones

[Vedthakar]

Can I work on this?

[etrepum]

This is a very low value and low priority task, that would be better done in conjunction with refactoring more of the code from plugins to extensions. I would focus on other issues.

[vadimkantorov]

Promoting mature playground plugins to extensions (or even a single extension) would be awesome too!