Use Monaco (VSCode editor component) with YAML language server

[drozycki]

I've just finished writing a non-trivial automation using the integrated text editor. As a professional developer unfamiliar with YAML and Home Assistant scripting, I found the experience to be frustrating. The editor lacks domain-specific schema validation, precise error highlighting, specific error messages, auto-completion suggestions, and reference tooltips on symbol hover and as you type - features common in modern development environments like VSCode.

I propose that we use the VSCode editor component monaco-editor instead. The monaco-languageclient package can run yaml-language-server in a Web Worker and enable those modern editor conveniences. yaml-language-server supports JSON Schema for domain-specific validation, and all packages are MIT-licensed.

The monaco-languageclient docs don't have a YAML demo but you can play around with their JSON demo here.