Simplifying Tool Icon Customization

https://github.com/codex-team/editor.js/discussions/1896

I've encountered an issue while attempting to customize inline tool icons within EditorJS. While simple tools with a straightforward structure allow for modifications using the toolbox or render, more complex tools like the Link tool present certain challenges:

1. Unnecessary copy of already built-in code implemented in EditorJS is required.
2. Even I just only want to change the icon, a significant amount of modifications is required in the copied code to align with the framework being used.

### The root cause of this issue is that the basic `inlinetool` class(such as `Bold, Italic, Link`) is not exported, leading to these problems.
Therefore, I propose expanding the export scope of default tool classes. By doing so, it would streamline the customization process and make it more accessible to modify these tool classes without resorting to excessive code duplication.
Thank you!