Lint XML (OSOE-716)

[Piedone]

Similar most to perhaps Markdown linting, we could have linting for XML files, at least for formatting, and ideally more.

Adding this in this project because Prettier can check the formatting of XML files with this community plugin. Related: #70 and #11. It's not a full linter though.

This would be interesting foremost for csproj, props, and targets files, so there's more to it than just standard XML linting. Thus ideally, we'd have dotnet/msbuild#1777.

Jira issue