3.0 rewrite

### V3 Beta is out! -> https://github.com/Ionaru/easy-markdown-editor/issues/447#issuecomment-5259503165

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**Is your feature request related to a problem? Please describe.**
Current codebase of the editor contains a lot of legacy code, is difficult to maintain and depends on a toolchain that is no longer optimal anno 2022.

This is basically my wish list for v3.0.

**Describe the solution you'd like**
A complete rewrite of the codebase, split code over multiple files, written in TypeScript and SCSS.

**Describe alternatives you've considered**
- Keep the editor as it is, difficult to maintain and improve, I don't think this is feasible long-term.
- Slowly migrate to more modern code by rewriting parts, chance of being stuck inbetween legacy and modern code is high. Also difficult to keep the editor working like it did with the old code.

**Additional context**

- Fully ESM (https://github.com/Ionaru/easy-markdown-editor/issues/262).
- Ability to only import parts of the editor that the user needs (https://github.com/Ionaru/easy-markdown-editor/issues/167).
- CodeMirror 6 (https://github.com/Ionaru/easy-markdown-editor/issues/324).
- Ability to use plugins (https://github.com/Ionaru/easy-markdown-editor/issues/391).
- Easier event hooks.
- No bloated icon downloads (https://github.com/Ionaru/easy-markdown-editor/issues/491)
- Ability to use custom icons (raw SVG?)
- No automatic textarea detection (no magic bahaviour / side-effects).
- Typescript
- SCSS
- Modern toolchain (~~Rollup?~~ Vite+)
- Updated standard look
- Standard dark mode
- Modern version of `marked` (https://github.com/Ionaru/easy-markdown-editor/issues/561)

**Progress**

You can follow progress on the https://github.com/Ionaru/easy-markdown-editor/tree/v3 branch.