feat(2d): add line counter for CodeBlock

[przemeksulecki]

I think it would be useful to add a feature that allows for retrieving the current count of CodeBlock's lines.

e.g. I'm using this for my custom 'CodeEditor' component that has numbering on the left side.

private createSideNumbers = (n: number): string => Array.from({ length: n }, (_, i) => i + 1).join('\n');
...
<Txt
     ...
      text={() => this.createSideNumbers(this.codeBlock().lineCount())}/>
...

BTW: When getting this value it has some delay. It could be probably improved in some way, but I'm not sure how.

[aarthificial]

BTW: When getting this value it has some delay. It could be probably improved in some way, but I'm not sure how.

This happens because during tweening, a temporary structure stored in this.diffed is used instead of this.parsed();
You could account for that by doing the following:

1. When tweenCode() is called, calculate and store the number of lines in the current source code and the new one.
2. In lineCount, check if this.progress() != null, and if so, use the progress to interpolate between these two line counts.

[przemeksulecki]

@aarthificial I applied your suggestions and looks good in my opinion.

[aarthificial]

Looks good! Needs just two little fixes