feat(language-service): support .vscode/settings.json html.customData

[Bomberus]

As mentioned in issue: #3975, many users still experience issues when they want to use custom elements via: vscode custom data definition (https://github.com/microsoft/vscode-custom-data).

This feature enables code completion for custom web components that do not have dedicated vue components (for example UI5 Web Components ).

This change will check if user has defined custom html data via .vscode/settings.json and load the files:

{
 "html.customData": [
        "./node_modules/@ui5/webcomponents/dist/vscode.html-custom-data.json",
        "./node_modules/@ui5/webcomponents-fiori/dist/vscode.html-custom-data.json"
    ]
}

Below short example how the editor will look like with and without these changes.