Enable syntax highlighting for XAML

[PiterGoCompany]

Please select if your request is either something new or an enhancement

• [x] Enhancement of an existing Feature.
• [ ] Request of a new feature.

Please select the area your request applies to. (Multiple selections are Possible. You can leave blank if you're not sure.)

• [ ] Workspace - VSCode workspace, vaults, Intellisense/autocomplete, Dendron settings
• [ ] Lookup - Dendron's Lookup Command
• [ ] Views - Dendron Preview, Tree View, Side Panels in the UI
• [ ] Schema - Dendron Schemas
• [ ] Pod - Data import from / export to Dendron
• [ ] Publish - External Site Publish
• [x] Markdown - Markdown features, such as syntax support and features

It would be nice to enable syntax highlighting for XAML code. Basic version can be the same as for XML syntax.