feat: implement multi-styled text shape

[Eywek]

fix #1131

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The idea of this new shape is to be able to render text with multiple styles (i.e. char 0 to 10 is blue, char 10 to 20 is black and with another font size).

I've used the Text shape and updated it to be able to support this feature. I've added more types than in the text shape (i.e. in getters/setters & context types) and tried to add all methods in the class.

To apply styles to the text you need to provide textStyles property for each text part. I'm not sure that was the best approach, but it was the easier in my use-case and I haven't found any other easy way to do it.

I don't know if @lavrton plan to merge this, but maybe it could help some people that need this feature.
Since the new shape use the same logic as the text shape (text wrapping, underline...) maybe it could be a good move to merge them.
I haven't done any tests (excepts manual ones, and everything seems to work) and I don't really plan to do any of them soon, I don't have really the time for it.

Anyone who want to improve this PR is welcomed (I've allowed maintainers to edit this PR but I also can add users to my fork is someone want to update the branch).

[lavrton]

@Eywek thanks a lot for sharing your work! I am going to think how to integrate it into Konva core. For now I don't want to merge with Konva.Text. Because it is already too complex. And supporting rich text inside it, will make it even harder.

But it may be a good idea for another shape.

[songispm]

something new? I need it.

[DavidVaness]

Any thought progress you can share on this feature @lavrton?

[aokaywe]

I neet this feature.

[lavrton]

Question to everybody who needs this feature. Do you need "read-only" multistyle text? Like a regular Konva.Text shape? Or do you expect some ability to change it with the editor?

[JamieBohannaWebDev]

For me, I think the read-only would suffice. I have recreated rich text (excluding multi styles for a single text shape) formatting by listening to QuillJS for formatting changes and applying them to Konva.Text shape manually each time.

[DavidVaness]

I have to agree with @JamieBohannaWebDev here, we are also using quill for the editor part.
The readOnly variant would already be really helpful to us

[joaodiogocosta]

Read-only 👍

[OtterlyOlive]

Any update on this? 😊
Read-only would be very very useful!

[5opr4ni]

Read only, would be most useful.