Add support for SVG files

[IvanGoncharov]

SVG files contain XML so it should be easy to add since Helix already supports XML.
I tried to add SVG support locally by adding following to my languages.toml:

[[language]]
name = "svg"
file-types = ["svg"]
scope = "svg"
injection-regex = "svg"
indent = { tab-width = 2, unit = "  " }
roots = []
grammar = "XML"

But it doesn't work 🤷‍♂️

[A-Walrus]

If we don't want to do anything SVG specific, I think we can just add .svg to the list of xml file extensions.