Support VSCode Custom Data, used in web-components libraries

[kt0]

Description

Currently only html custom data provided by (vscode-language-server)[https://github.com/microsoft/vscode-html-languageservice/blob/main/src/languageFacts/data/webCustomData.ts] is supported, it ignores html.customData vscode configuration entirely.

This causes annoyance when using webcomponents libraries, e.g: ionic, shoelace-style.

Proposed solution

For example this vscode config is suggested for shoelace-style:

{
  "html.customData": ["./node_modules/@shoelace-style/shoelace/dist/vscode.html-custom-data.json"]
}

It works for html files but not in svelte components

Alternatives

No response

Additional Information, eg. Screenshots

Volar supports this

P.S. I looked into the code and tried to implement this but it requires quite big changes, so I stopped.

P.P.S. I do not not know how this affects other editors (nvim, helix, etc) using lsp (if html.customData is a vscode thing only or other lsp users also use it)