feat(markdown): SVG extension

[gfanton]

This is a draft PR aimed at improving SVG handling by creating a dedicated Markdown extension. It will specifically enable the handling of links within the SVG. Unfortunately, in it's current state it alsoallows JavaScript injection, which is a no go for now.

following and closing #4479

[Gno2D2]

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[codecov[bot]]

Codecov Report

:x: Patch coverage is 92.40506% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gno.land/pkg/gnoweb/markdown/ext_svg.go	92.10%	6 Missing :warning:

:loudspeaker: Thoughts on this report? Let us know!

[jefft0]

@gfanton , how is this related to https://github.com/gnolang/gno/pull/4771 ? Should it be merged into this PR?

[gfanton]

@jefft0 No, there is nothing related to #4771. The goal of my PR is to implement a way to support SVG without using images, primarily to enable linking within SVG.

[vikbez]

Why both <gno-svg> custom tag + <svg> tag ? (btw if you close with </svg></gno-svg> it fails rendering, you must close with </svg>[\n]</gno-svg>)

SVG is difficult to implement as 100% safe - here is some reading

For safe SVG+links I can only think of parsing and only allowing elements we want with something like bluemonday

I had another idea but after trying I found that it does not work 🥲

Except for this your implementation works with what I tested :+1: